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G3 Dmr Build: A Quest For The Perfect Pew Pew!


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#1
TotalNick41

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Hello,

I am not sure if this is the right section to post this thread in but thought i'd give it a shot.

(BACKSTORY)
My name is Nick, Location: 1 hour west of Indy. I used to be into airsoft when I was a kid, but have recently wanted to rekindle my love for the hobby through my current career in government security/law enforcement as a young adult.

(PREFACE TOPIC OF THREAD)
I have been slowly going through my old gear, updating/combining it with my current work gear, and ordering new products to fall in line with the rules i've seen on a few airsoft fields' websites I plan on attending. This brings me to the purpose of this thread.

(TOPIC OF THREAD)
The old gun I used to rock was a JG G3 RAS. It still shoots as well as I remember it did back in the day and I plan on running a G3 setup with my future involvement in the hobby. The problem is the rules on pretty much all of the fields i've looked at classify this gun as a DMR. So it looks like i've got some work to do.

Here comes the part where I need your help. I have been trying to look up everything I can about tech work and upgrading my specific airsoft gun for a few weeks now and am completely lost on all of it. I have read through the "Holy Grail of Building Your DMR AEG"- (https://www.airsofts...pics/892?page=2) thread a few times now but still came out clueless and a complete noob. I do not have any experience in this field and thought about sending it in to a big box airsoft store (Airsoft GI, Evike, etc) to do the tech work and upgrades for me, but have read a lot of poor reviews on their services/parts and assume they'd try to overcharge me. That is when I stumbled upon this airsoft forum and saw that you gentlemen could possibly help me/inform me on what RIGHT parts I would need for this build and even some outlets for possible tech work within the state. So my question is, what do I need/who will help me build my perfect pew pew?

What I have:
-Stock JG G3 (RAS)
*not going to include accessories in this section*

What I would like:
-Reliable airsoft gun that I don't have to tinker with
-Proud rifle that fits the bill as a TRUE DMR
-Product that falls within regulations of common airsoft fields/events
-Someone within Indiana who could perform paid tech work for me
-Have read that I need to "permanently" alter my gun to semi-auto for a DMR. Is this something I do/take out internally in the gun or is a selector switch set to semi-auto all that is required?

Other than that, I am all ears and open for suggestions. Budget is flexible but am wanting to stay within reason.

Lastly, I have a question about the rifle itself to base this build off of. As stated above, the gun I preferred to start this build with was a JG G3 since I already own it. But, since I am not well versed in tech work, upgrading guns, and pricing a project of this nature, would it be more cost effective for me to just purchase a newer replica G3 on the market such as the LCT version rather than trying to upgrade an older gun like the one I have? Or would I still need to upgrade an LCT G3 abunch to perform at DMR standards and end up going way more over budget than if I just stuck with the JG G3? I am just trying not to polish a turd here for lack of better words... Also, I have recently purchased all new Classic Army G3 mid cap mags to conform with field regulations. They fit my JG but am unsure if they would fit an LCT G3. I would hate to have to drop even more cash on buying more mags so if anyone knew if they are compatible that would help sway my decision.

Sorry for how long this post was. I hope it finds you all well. I am eager for a reply and will standby for your thoughts and advice.

Thank you,
Nick

References of other JG G3 builds online:
http://www.airsoftgi...opic.php?t=6313

https://www.airsofts...d.106429/page-2

http://www.airsoftfo...-g3-into-a-dmr/

https://www.google.c...es_for_a_jg_g3/
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#2
green gaint

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There are some guys here on the forum that do good tech work, check out the verifed tech list for it. Consider checking out brillarmory.com for your parts, just about all he sells is decent stuff. Keep you jg, upgrade just about everything, gears, motor, piston, compression parts, hop up and barrel, and you may wanna consider a mosfet
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#3
Hanback

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Whatever you do, do not send your gun to a big box store for tech work. The sheer number of guns that go thru those shops means that they are unable to spend much time on individual guns and with thet many guns on a daily/weekly basis, the desire to take that extra effort on a build is seldom there. Ive been through it from the Tech's end, so I advise you not to. Plus, the price you will pay will be exuberant.

 

Find a local reputable tech or small local store that does tech work and use that as your route, Better customer support, better attention to detail, and better all around process.

 

As to what all to do, I dont have the time this evening to write it out for you, but if you search around thru the AEG discussions and AEG gun tech sub-forums there should be a number oid threads concerning DMR type things. I know I have responded to numerous throughout the years. Linked below is one in particular from just a quick search. Keep in mind these are old threads and there is new info in the past few years to account for.

 

http://www.airsoft-i.../5869-dmr-help/

 

If i get a chance tomorrow or Wednesday evening I will put together something more specific for your above purposes.


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#4
Nox

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So I'm gonna answer stuff as i go...

 

1) This section is fine. You gucci

 

2) I heavily recommend watching teching videos on youtube. A lot of people struggle with learning how to tech until they can actually see what is being explained or how to do something. TheAirsoftTech makes great videos.

 

2b) Don't send it to a big name store. Umbrella Armory is the only one that would really consistently put out quality work but even they have started dropping behind. BG Airsoft down in Kentucky does custom work and has a great reputation, but, like mentioned by others, there are quite a few techs listed on this forum that you could contact.

 

3) With a solid DMR build, you are pretty much going to replace almost everything inside the gun, so when it comes to whether you keep the JG or not, all you need to consider is: Do you want your gun to feel like the real deal (quality metal body, real wood, much heavier, very sturdy)? Do you want to spend the extra money just to have better externals?

 

4) As for the semi auto thing, permanently semi auto generally means that you can't switch your gun back to full auto at the event. Now, there is no true "permanent" semi auto cause someone could reprogram their mosfet, or bring an unmodified selector switch and switch it out in the field, etc. The idea is that your gun has been made to only shoot semi auto and that it will be difficult to undo. The best method IMO is to get a programmable mosfet like a Gate Titan or BTC Spectre/Chimera and set it to only allow semi auto. This is the most expensive route but provides a necessary trigger contact upgrade, solves your semi auto need, provides battery protection, and much more.

 

All that being said, the project you have in mind will be fairly costly in parts and labor, but is relatively simple in the world of teching and you should have no issue getting it done. I can get more in depth on all the parts and modifications if need be.


Edited by Nox, 26 November 2018 - 09:51 PM.

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#5
TotalNick41

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Wow, thank you all so much for the advice! I think I am going to contact one of the techs from the site and get his input on what he thinks I will need/guide me in the right direction as far as parts go. I am going to check out that Youtube channel and site you guys mentioned and try to "get guud" at my knowledge of airsoft tech.
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#6
Hanback

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Alright, apologies for the delayed response. This is a condensed (seriously) version of my documentation and information from answering similar questions over the years. A lot has changed over the years on the process to do this all, so I try to hit on everything as it currently stands.

Other techs, please feel free to chime in with any input from your end.

For those of us here in Indiana and the greater Midwest, the regulations around DMR’s fluctuate between games, locations, EO’s and Field Owners. For the most part though, fps of a DMR is measured between 420 and 450 fps on 0.2g bbs. More recently this has changed to a joule limit to prevent joule creep issues in running overpowered 0.2g setups that push a heavier bb with greater force. For those that don’t know/understand this issue, refer to section 4.6 for more info and links. Depending on the field, the joule limit is 1.65 - 1.8. Thus, any DMR you build should abide by the joule limit as opposed to the fps since DMR guns are typically running 0.3g and heavier bbs. If you are running <0.3g bbs in a DMR, you probably need to completely rethink the whole DMR stance.

Also, most fields and events will restrict DMR’s to guns in real life that are actual DMR’s. Much like an M4 with a box mag is not a support weapon, an M4 with a barrel extension is not a DMR. When you think DMR, think primarily in the 7.62 variant caliber style guns. But, you do you.

So, what needs tracked when building a DMR? Everything. Ill break it into 5 parts, listed below.
Part 1.0: Permanent Semi-auto
Part 2.0: Gearbox Power
Part 3.0: Compression
Part 4.0: Strength
Part 5.0: Consistancy/Range/Accuracy

1.0 Permanent Semi-Auto
First and foremost, you need to be “permanent” semi-auto.

1.1 This is achieved in one of two manners; either mechanical or electrical. The easy and cheap option is the mechanical route. A quick simple modification to the selector plate can cause permanent semi-auto. Easy as that. Upside is that it is quick, easy, and free to do. Downside is that lockup with a disengage trigger contact is possible if we are talking v2 platform gearbox here. This takes partial to sometimes complete disassembly to unlock the gearbox should it occur. There are ways to avoid lockup, but it may take some retraining of the trigger finger. ICS operational forward assist on AR models eliminates this, but, seems to be a rare thing these days. Lockup isn’t so much an issue outside of the V2 gearbox realm.

1.2 Option 2 is electronic controlled semi-auto. This is achieved thru the use of a programmable mosfet. The upside is that with an electronically controlled setup, there is no need to worry about mechanical lockup. The downside is that this route is expensive, in excess of $100 simply for the mosfet itself. Additionally, mosfets can be touchy and are not hard to break. Most utilize very high gauge wire that is susceptible to breakage, pinching, etc. which can destroy the system itself. You will want to always assemble and disassemble gently, taking care to ensure no damage to the wiring and electronic parts. Also, ensure the main control circuit is out of harm’s way, shielded from the sun, rain, snow, and any dust intrusion as well. All of these are severely detrimental to electronics

Whichever route you choose, both achieve the semi-auto part.

2.0 Gearbox Power
The second part of a DMR is the power of the gearbox.

2.1 You will be using an m130-m140 spring depending on the rules/regulations that you are building to. Back in the day, the method of powering the gearbox with these strong springs was to utilize torque up gear sets that were 20:1 ratio and larger. This increased the mechanical torque which meant that lower powered and weaker motors could still power the gearbox and pull the spring with ease. The downside to this was that cycle times of the gearbox itself were not quick, and would be higher than a stock gun because of the large ratio gearset. The motor has to make more turns to cycle the gearbox just once.

2.2 Technology has come a long way in recent years and the guidelines have changed though. Stronger torque motors are now produced, and for less expensive prices, meaning that higher ratio gears are no longer as necessary to achieve similar mechanical torque values. In more recent years, motors such as the G&P Devil Jet and G&P Satan Motors (and similar other makes) are now out that are capable of pulling M160+ springs on standard ratio gearsets at very high cyclic rates. In short, super strong motors allow you to utilize a very low ratio gearsets (13:1 - 14:1) and high power springs since the motor itself is producing significantly higher torque numbers. By powering low ratio geats, this minimizes gearbox cycle times, which in turn produces better and faster trigger response times. The motor spins less for a single gearbox cycle. Thus, a properly paired motor and 14:1 gearset will power an m140 spring in excess of 28rps if desired.

2.3 Example: Four years ago while in Florida where ridiculously hot polar stars were running rampant, I built what was titled the “Polar Star Killer” for a customer. With a set of 14:1 SeigeTek gears, a G&P Satan motor, ceramic bushings, and my custom wire harness, I was able to make an M14 EBR gearbox cycle an M170 spring at 28.5 RPS. It was ridiculous. As to how the gun was used and fielded I cannot answer, I simply built to the customers’ requirements and provided a gun to outdistance and outshoot a 600 fps Polar Star. But the point stands. With high powered motors, there is no longer a need for high ratio gearsets. The downside to these high powered motors is that they are often battery hogs. In order to produce the necessary electric field to spin the electromagnet at the desired power, a very large amount of electricity is required. This in turn can reduce battery field life by as much as half.

Think of it as your 4 cylinder Honda coupe vs you big block Mopar vehicle. You want the fastest 0-60 time (your gearbox cycle time) and while the Honda can do it pretty well, the 4 cylinder isn’t going to get there as fast as the big block, which will achieve that in the blink of an eye. But then, how much gas did the Honda use vs the big block? Chances are the Honda can do this 0-60 haul probably twice as many times as the big block before it runs out of fuel. Now back to airsoft motors. That high torque monster neo-magnet motor will yank that spring no problem, but it won’t be able to do it as many times as that low end ferrite-magnet motor. So keep it in mind, as the difference will be noticeable. Me personally, I get about 1200-1300 rounds on a single 1200mah 11.1v lipo and that’s it. Those thousand rounds are quick and instantaneous though. Running big brick lipos though will likely negate this issue entirely.

2.4 The spring. Most typical DMR’s will run springs in the m130 - m150 range, and actual power varies based on manufacturer, manufacture technique, and design. Variables of rung thickness, free length, pitch, rung per inch count, and material properties such as elasticity and stiffness all very widely between manufacturers. The big thing when it comes to springs though is pitch, and liner vs nonlinear pitch springs.

2.4.1 A linear spring is exactly that, a spring with a constant pitch between rungs. They typically run a bit hot when first installed before settling down once broken in. The upside is that they retain their power and stiffness well, even after years of repeated abuse. The downside is that the force to displace the spring is a linear relationship to the magnitude of displacement of the spring. Most AEG motors require a wind-up time from the time the circuit is completed and the motor receives power to the time the motor is producing its maximum torque, and with this linear force displacement relationship, the motor can struggle while initially pulling the spring, leading to an increased gearbox cycle time. This is most notable with lower end ferrite motors, and the whine they produce upon startup.

2.4.2 Nonlinear, irregular pitch springs utilize a non-constant spring stiffness constant (k) that varies based upon the magnitude of the displacement. The initial compression of the spring is done so easily before the stiffness increases, and the force to continue displacing the spring multiplies exponentially. The upside to these springs is that the initial easy compression prevents the motor from struggling to pull the spring upon startup, and allows the motor to reach its maximum torque producing point before introducing the significant spring force the motor has to then compress. This allows low end motors to be able to easily and effectively pull these m120+ springs, and with the meat of the pulling occurring while the motor is experiencing max torque, the gearbox cycle can be completed more quickly since the motor isn’t struggling against the spring to get the point of maximum torque. Also, the springs typically don’t come in as hot as liner springs when initially installed. The drawback to these springs however, is that because of the very low initial stiffness and un-uniform loading characteristics, they wear out and loose power much more rapidly than linear springs. Additionally, if the circuit is open partway through a cycle and the motor only pulls the spring halfway back and then stops, depending on the motor, it may likely be unable to complete the cycle as it is not able to generate its necessary spin up to maximum torque with the partially compressed and significantly higher resistive spring force to pull. Lastly, when paired with very high performance motors, nonlinear springs can lead to over cycling of the gearbox and loss of control. Upgrading the motor in stock late model (2011-2014 era) KWA’s was known to cause a “tick-tok” effect that would be a 1.25 gearbox cycle, followed by a 0.75 gearbox cycle, despite a powerful m120 being installed. Rapid shooting resulted in a “tick-tok” sound of over cycle, under cycle, over cycle, under cycle, and on it would go. This was very noticeable when powered by 11.1v lipos.

2.4.3 So in terms of a DMR build, it is best to shift focus to a liner spring of constant rate and pair it with a very strong motor that won’t struggle on spin up. With the afore mentioned method of low ratio gears and high output motor, you should already be looking at motors more than capable of handling this spring during spin up. However, should you find yourself unwilling to drop the cash on a high dollar motor or experiencing issues with initial pulling of the spring, you can rectify the situation with a nonlinear spring.

2.4.4 Also with respect to compression, a typical liner spring will cause a gearbox to run hot when first installed, and requires a break in period in which the spring will experience enough creep to settle down. For a liner pitch m120 spring, they can come in as hot as 425 fps (on 0.2g), but after break in can settle out to a very consistent 390-400 fps (on 0.2g) and hold this mark for years. A nonlinear spring will not run as hot when first installed and does not require much, if any break in period to become legal to use. However, it will still go thru a similar break in period and experience some creep, after which you will find yourself anywhere from 15-40fps below the mark that you want. Depending on the requirements of your build, this alone may cause you to sway one way or the other. A broken in but under powered spring can be remedied by adding washers to the spring guide, but this isn’t an exact science and will require trial and error with some math and a chrono to get right.

3.0 Compression
Part 3 is the system compression throughout the gun.

3.1 With a DMR you will want as consistent compression as possible. This means that you want a good CNC ported piston head, and CNC Double O-ring sealed Cylinder head. Additionally, an O-ring sealed air nozzle is desired as well. Ensure that all compression components are of metal make (explained further below in sections 4.1 and 4.7.4). As to the O-ring to use, I suggest only going with Kimball Midwest #14’s. It is the proper inner and outer diameter you need, and Kimball Midwest rubbers are designed for the automobile and agriculture world which is much more taxing than airsoft. The O-rings are mostly unaffected by cold weather too. I have Kimball Midwest O-rings still going strong now even after 6 years and 500k rounds.

3.2 The Cylinder. This is vital as it is where the piston does its work, and the volume of this is what is most important. There are multiple types of cylinders designated by their ports which all determine the volume ratio (refer to section 4.6) to mate to the barrel. Given the typical configuration of a DMR rifle (long barreled rifles), you should only be using non-ported type 0 cylinders, especially if running sorbo pads and AOE mods. Additionally you want to ensure the inner finish of the cylinder is pristine. This will aid in compression consistency and prevent O-ring wear and failure.

3.3 Word of caution. Avoid Bore-up kits at all cost. Then increase the volume of the cylinder by enlarging the inner diameter of the cylinder itself. Smart thinking right? The problem is that now the cylinder requires a custom/proprietary O-ring, and given that these O-rings are specific for airsoft, they are made from low grade materials/quality and will not last long. Once you lose compression, now you have to find another “special” O-ring. And no, you cannot go to a hardware or special O-ring store to find this specific O-ring. You are pretty much required to find an OEM for the setup, which can be nearly impossible. It is best to avoid this whole avenue and prevent any future problems.

3.4 Just as important as gearbox compression is hop-up compression. However, due to the nature of this discussion, we will touch on it below in section 5.0.

4.0 Gearbox Strength
Part 4 is strength of the gearbox and all internal components.

4.1 Plastic parts will work, but with the increased forces acting on the parts from the heavier spring(s), these parts will flex in tension and compression at a greater magnitude and wear out much quicker. This is especially important for compression components (piston head, cylinder head, and spring guide). Look for CNC aluminum to keep weight low and strength high. Additionally, ball bearing springs guides and piston heads allow the spring to twist freely within the gearbox and minimize rubbing and grinding on these parts which will reduce wear and extend the life of these parts greatly.

4.2 Ball Bearings for the gears are ok to use for <400 fps setups, but not so much for >400 fps setups. Ball bearings reduce friction and thus rotational drag which is good, but they introduce small amounts of side to side play which you want at an absolute minimum with heavy spring setups to prevent premature wear on gear faces and teeth. Also, ball bearings take a lot of torsional loading, the magnitudes of which increase non-linearly with spring strength, and it is this torsional loading that wears the bearings out. When a ball bearing starts to wear out, it gains significant play, and the greater the play in the bearing, the even faster it will continue to wear until complete failure. When a ball bearing experiences complete failure, you can kiss you internals goodbye as it will take out gears and more when they finally give.

4.2.1 The smartest choice is ceramic bushings. They are designed for torsional strength and can take significant abuse. They do introduce more friction into the rotating setup, but not at the expense of wear on the gear posts themselves like metal bushings will do. Additionally, it is rare for ceramic bushings to fail spectacularly, as they fail much slower and a much lower risk to damage of other parts. It is important to maintain regular inspections for looseness of the gear posts within the bushings as well as any bushing wear that will cause an increase to gear lash.

4.3 As for gearbox shell, just about any V3 gearbox shell will be capable of anything <500 fps. In the V2 platform, you must have a high end reinforced gearbox shell to handle the abuse. Rounded corners on the cylinder corners of the shell are a great indication that the shell can handle large amounts of stress. Regardless of what shell you choose, you will need to check the fitment of the bushings. If the bushings easily fall out of the shell then the shell itself is worn out, and should be replaced. The bushings should press firmly into the shell itself and remain tight within it. Any amount of play will be detrimental to the life of the gearbox and can cause premature wear on the gear set.

4.4 Lastly, the piston. Many people believe that full metal pistons are the best choice. Don’t fall for this thinking. Often, these people experience excessive wear and piston failure repeatedly from a particular setup and chose to swap in a full metal tooth piston to solve this. Although faulty parts are certainly possible, excessive wear and repeated piston failure is indicative of problems with the gearbox itself. Simply swapping in a metal piston doesn’t solve a thing, but instead moves the failure point. Excessive piston wear and failure is attributed to improper AOE. A polycarb piston is more than capable of pulling heavy springs repeatedly and for years without issue if properly tuned.

4.4.1 Think of it this way; the piston is plastic for a reason. If anything with the gearbox is wrong, it is the $15-30 piston that will take the fall and break without causing damage to other components. This is by design and your sign that something isn’t aligned right. Now if you swap in a full metal piston without doing anything else, you have strengthened the failure point beyond its design. If anything is out of line or not right within the AOE, the piston will no longer fail and protect the other parts by doing so. Rather, the piston will cause the increased stresses to be offloaded onto other parts. When left unchecked over a timespan of use, this causes excessive wear on these other components until the failure point is reached. Now instead of a $15-30 part breaking, you are breaking your $50-150 gearset, causing irreparable damage to certain gears, damage to the gearbox shell at the bushing areas, etc. Your quick fix of swapping in a metal tooth piston literally solved nothing, and caused significantly more damage in the long run.

4.4.2 So, in DMR speak with heavier springs and higher stress concentrations, what does this mean? With the exception of section 4.4.3 below, try to maintain a polycarb piston, BUT, because of the stronger spring, ensure that at least the last 5-6 teeth are metal. Typical stock pistons have only the last 3 teeth metal. These 5-6 teeth need to be metal to hold up to the increased strength of the spring when fully compressed. All teeth behind it should be polycarb though as a protection. Next, get a sorbo-pad and neoprene pad. Attach these to you cylinder head permanently, and then while gently pressing the piston forward into the cylinder head to simulate a small spring pre-load behind it, measure where the sector gear contacts the piston, and begin to gently shave off teeth until the first tooth of the sector gear is able to rotate unopposed to the back of the piston, and the next two teeth rotate to engage the now modified piston teeth.

4.4.3 Now, I don’t write off full metal rack pistons entirely, as they have their place, but in a different aspect. The importance of these full metal pistons is their weight, and refer to section 4.7.4 for further explanation. The strength of these pistons is also necessary for >600fps builds. Full metal pistons can be unforgiving though, so you need to be 100% certain that the AOE is absolutely perfect and that additional lubrication is used on the piston to sector gear interface. Sadly a number of OEM’s (LCT for example) now build gearboxes with full metal rack pistons on factory tunes (not great) and I have seen numerous catastrophic failures with these setups.

4.5 Now, specifics on the sorbos. Not everyone runs them, but they are highly suggest for 3 reasons. First, as explained above, it allows you to completely reset the AOE to perfection. The importance of this speaks for itself. Secondly, it acts as a buffer to slow down the piston impact and reduce the shock, transmitting the energy from the piston to the shell over a longer timespan that then reduces shock stress and can prolong the life of the gearbox shell. Lastly, and mostly a side effect, adding a sorbo has an acoustic effect on the gearbox. If you are looking to build a quiet DMR, this is the primary method to reduce compression system noise (there is more to it than this though).

4.5.1 There are typically 2 thicknesses and 2 stiffness’s to choose from. Typically you can get 1/8” and 1/4” at a 40D or 70D stiffness. The stiffer the pad (70D), the less damping effect it has, but the longer it lasts. The softer the pad (40D), the more dampening effect it has, but the shorter it will last. The old rule of thumb was to replace the sorbo in conjunction with the primary O-ring, but advances in O-rings have rendered their lifespan into the 3+ year range now, so you can’t do this so much anymore. A better rule of thumb is to replace the sorbo roughly every 2 years depending on use and condition. Keep in mind though, just because the sorbo looks visually fine, does not mean that it is good. Its dampening effects may be all but gone from repeated compression abuse.

4.6 Cylinder to barrel volume ratios. This is something to keep in mind when using sorbos. Optimally, you want your cylinder volume and inner barrel volume to maintain a ratio around 2:1 for a DMR running 0.3g bb’s. This is optimal, but in practice the range you want should fall between 1.8:1 and 2.2:1. To really get into the science behind it, I refer you to:
http://airsofttech.d...rVolRatio_Page1
https://www.airsofts...-explained.html
At the top level, in that range you are neither under powering nor over powering the bb. Under power (<1.8:1) will lead to complete inconsistency in fps, bb flight, and range. Over power (>2.2:1) leads 2 things. First off, it means that there is excessive remaining pressure behind the bb even after it has reached the exit of the barrel, and this can cause inconsistent flight path and range. Secondly, this is capable of leading to Joule creep, a topic not even known by much of the airsoft community, but a very serious and sometimes dangerous thing. Refer to below for more info:
https://www.airsofts...-creep-aeg.html
So assuming you are aiming at 0.3g bb’s, you want to maintain a volume ratio as close to 2:1 as possible. Now, adding a sorbo pab to the cylinder head reduces the cylinders inner working volume. Negating compression effect of the sorbo itself (smaller volume when compressed vs uncompressed), this will reduce your cylinder inner air volume, and in turn reduce the volume ratio. This must then be counter-acted by modification of the inner barrel to then regain that volume ratio. The inner barrel can be shortened, reduced in inner bore diameter, or both.

4.6.1 For example: Let’s say you have a non-ported type 0 cylinder in a G3. It has a cylinder length of 72mm and diameter of 24.03mm. Your cylinder head has a nested depth of 7.25mm and piston head has a depth of 6.0mm. In stock configuration, this means that you have a cylinder working length of 72 - 7.25 - 6.0 = 58.75mm which when multiplied by the cross sectional area gives you a working volume of 26644.4mm^2. Let’s assume your stock barrel is 465mm in length and a 6.04mm bore. This nets a barrel volume of 13323.5mm^2. Thus your stock ratio is 26644.4:13323.5, or, 1.99:1, which is good.

4.6.2 Now let’s say you add a 1/4” sorbo. Sorbo+neoprene pads comes to a height of 6.35mm. This needs subtracted from the working length of the above calculations, bringing our new working length to 52.4mm and a working volume of 23764.5mm^2, which is a ~12% difference. This now leads to a volume ratio of 1.78:1. In reality this is still in the “ok” zone, but we still want to maintain as close to the 2:1 ratio as possible, thus you will need a different barrel of differing length, bore diameter, or both. It may take some math to figure out, but it is well worth it. Once you have everything paired properly, consistency of the system will become golden.

4.7 The other major effect here is a lot more in depth and hard to work with. The most efficient setup is one in which the bb reaches the end of the barrel at the same exact moment in time that the piston reaches the end of the cylinder. A short barrel can yield a piston that has not completed a full stroke before the bb leaves the barrel, and a long barrel can yield a piston that has completed a full stroke prior to the bb leaving the barrel. This becomes a very hard thing to predict and plan around, but its effects can be noted when the two are substantially mismatched. The method to solve this is to control the weight of the piston in conjunction with the weight of the bb and the barrel length. The lighter the bb, the faster it will reach the end of the barrel. The heavier the bb, the longer it takes. For a DMR, you want bb’s no lighter than 0.3g, so you need to appropriately build a piston to match this such that the heavy piston reaches the end of the cylinder at the same time that the heavy bb reaches the end of the barrel.

4.7.1 Keep in mind, when properly designed, this is built for the best efficiency ONLY for the bb weight you used in the design. If you decide to change the bb weight, you NEED to adjust the piston weight accordingly as well if you want to maintain the efficiency. Many believe this step to be a bit over the top, and for the run of the mill gun build, it typically is. However, the point of a DMR is to be such a fine tuned machine that it can easily outshoot non-DMR’s, thus this becomes an important factor when designing your DMR. The problem is there is not an exact science to it and much like engineering in general, there is no exact answer, only approximations.

4.7.2 The calculations for this aspect go far beyond that of the volume ratio, and become complicated very rapidly. Along with tracking volumes of the cylinder and barrel, you have to take into account both static and dynamic pressures between the barrel and cylinder as well as time of travel of the piston and bb, of which travel time of the piston is dependent upon the spring constant via hookes law. The problem is that there is no specific spring constants listed per springs (m120, m130, m140, etc) and measuring this value experimentally is not always easy. There are ways though. To make matters worse, most springs now are non-linear to allow for an easy initial pull while a lower end motor is still spinning up to strength. This means that the spring constant is technically not a constant value, but rather a function of displacement. Thus, the force of the spring is a nonlinear relationship to the magnitude of its displacement, and mathematically this simple equation becomes a differential, represented graphically via an exponential function.

4.7.3 In other terms, this means that once the spring is pulled back, as it is released, it accelerates forward and a non-linear pace. In order to accurately determine the time it will take to cover the working distance of the cylinder, a simple equation cannot be used, and a differential equation is utilized to model the displacement with respect to time, acceleration, and velocity, all of which is solved via integral calculus.

4.7.4 I won’t get into insane specifics here. This is a primarily unknown area to 99% of airsoft and where I am already working and have been working for a while now. In short, the longer your barrel is and the heavier weight bb you use, the heavier you will want your piston to be. You can achieve this thru the use of metal piston heads, additional washers on the piston that weight it down, heavier weight piston constructions, and so on. Don’t overkill it, but for 500mm inner barrel on 0.35’s, weight that piston down as much as you can. This is where full metal pistons come into play. The weight of these pistons can give you the outcomes that you want for a very long barreled build that is using very heavy bbs. Again though, you must be 100% certain of the AOE and lubrication, otherwise this option can easily wreck a gearset.

5.0 Consistency
This leads us into part 5, consistency, range, and accuracy of the system

5.1 We have already touched on it up above, but only in terms of the gearbox. Now we speak in terms of the hop-up and barrel. First and foremost, everything you do in the gearbox to aid in compression and consistency is null if you don’t match it all to a good hop-up. Without a good hop-up, nothing explain above will make a damn bit of difference. When it comes to the hop-up unit, anything CNC is what you want. More often than not people forgo the hop-up in favor of the barrel, the bucking, and other aspects. Although these will all certainly help, just like the work done inside the gearbox, they mean nothing if not paired to a proper hop-up. The hop-up unit is the heart of you consistency and accuracy. A good hop-up with a shit barrel will out range and out-perform a bad hop-up on a good barrel. Should I say it again?

5.1.1 There are numerous highly engineered hop-ups on the market now that are good. They will range in value from $25 to much more. The cheapest hop-up unit you should be using is a Pro-win. For the AK platform, I HIGHLY recommend the new Retro-Arms CNC units. They put the Pro-Wins to shame, BUT, can require minor modification for fitment. Same with the Retro-Arms M4 hop-ups. The big difference is that these lock into place and will not back off with use, causing you to have to adjust the hop-up every few hundred/thousand rounds. Whatever you do, look for CNC units and not injection molded or cast units. You want tight tolerances and good finish.

5.2 From there, you want a good bucking built for your weather. Krytac orange and G&G green buckings are cold weather capable that don’t get hard and shrink in cold weather. They are like all-weather, all-terrain, all-season tires. Other buckings are better in certain conditions, but only those conditions for which they are designed. You never put a snow tire on hot pavement in July, or drag slick on cold wet pavement in March. These conditions are not what the tires are designed for. Likewise, you don’t take a Prometheus purple into the dry cold January air, and the analogy goes on. Determine the bucking you need based on you region and play. The afore mentioned all season buckings are good all arounders.

5.3 Now you want the hop-up nub. Without going into the physics and everything else, your best bet is to R-hop the setup9 R-hop, M-hop, Flat-hop, etc). There are numerous how-to’s for creating this setup, but we also happen to have the foremost tech on the subject here in Indiana with us. Depending on your desire, it might be worthwhile just to have him do the work.

5.4 Lastly, the barrel. You do not “need” a top of the line tight-bore. A properly set-up compression and hop-up system can render the same outcome whether you are using a 6.02 Stainless Steel or a 6.04 brass barrel. The only real important part of the barrel is the bore, and only because it plays into the volume ratio explained earlier. Contrary to popular believe, the bb theoretically never touched the walls of the barrel. Rather, it rides a cushion of air all the way down the barrel. More practically, given the magnitude of the backspin placed on the bb, it may ride the very top of the barrel. Working in theoretics here though, you still want to ensure there is a pristine finish on the entirety of the inner barrel surface, but this is for the air flow, not the bb. The smooth, clean surface promotes a more laminar flow down the barrel which, although not drag efficient for the bb, ensures that it floats consistently without touching the walls of the barrel. Rough and dirty surfaces create separation points in the flow that induce turbulence, which in turn can affect the smooth transition of the bb down the barrel. Additionally, rough and dirty surfaces can cause minor inconsistences in the cross-sectional area of the barrel which can create very small venture effects that affect pressures down the length of the barrel, again effecting the flight of the bb. What you want is a smooth and steady pressure decrease as the bb moves down the barrel.

5.4.1 So, in short, so long as the barrel you use has a good inner surface, don’t buy into tight bores and stainless steel and such for the wrong reason. Rather, mate your barrel to you cylinder properly for bore and length. Obviously an M14 has a longer barrel, and thus a higher barrel volume. Reduce this volume by using a tight bore in the m14 to yield a lower barrel volume if you add a sorbo to the gearbox. Conversely, use a wider bore barrel in a short AR pistol to increase the barrel volume to the proper ratio to mate to the gearbox cylinder. Make sense?

The last thing I will touch on is lubricant. White lithium used to be the king, but white lithium attracts moisture and breaks down as it absorbs it more. The only lube you should use on compression components is silicone based lubricants. Likewise, silicone lubricants are good for gears as well so that you can avoid the mess of white lithium. I am not talking silicon oils though, I am talking silicone grease, like dielectric grease. Plain jane SuperLube is all you need. Other options include tephlon grease and Krytox, if you have access to it. I have found Krytox to be the absolute best and longest lasting, but, its hard to get hold of and is absurdly expensive. SuperLube gets the job done just fine and doesn’t break down easily.

So, long read, but I hope it answers questions you both had, and didn’t know you had. Let me know if you want specifics on anything.

-Hanback
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#7
TotalNick41

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*Tons of useful information*

-Hanback


Wow thank you so much! I really did not expect this much advice, I really do appreciate it, truly. Answered a lot of the questions I had!


Edited by hrturner, 07 December 2018 - 09:13 AM.
Shortened quote to keep page from being unwieldy

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#8
hrturner

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Wow thank you so much! I really did not expect this much advice, I really do appreciate it, truly. Answered a lot of the questions I had!

Hanback always has good info (as does much of the forum, :lol: )


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#9
Nox

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Hanback, the one thing i will comment on is the G&P Satan motor; don't buy it lol. For that price, you could get a StarWei or Action Army motor that will be of significantly better quality, or even for half the price you can get one of the ASG CNC'd motors which also work extremely well.

 

Great write up though!


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#10
Hanback

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Hanback, the one thing i will comment on is the G&P Satan motor; don't buy it lol. For that price, you could get a StarWei or Action Army motor that will be of significantly better quality, or even for half the price you can get one of the ASG CNC'd motors which also work extremely well.


Fair input. The G&P's were the first that came to mind when writing it up. To be fair, even those are technically "out of date" by this point. Plus the G&P's never seem to last long, at least not when in "performance mode." I suggest just about any other motor as well.

I experimented briefly with a Tinely for a short bit. Good CNC motor, but it just didn't quite do what I personally wanted it to do. I'm also super pickey though.

Old Systema Magnum motors work fantastic for this and run like a raped ape, but they also sound like one too....not optimal in a "quiet" build. And they are battery guzzling monsters.

I still to this day run CA Extremes from like '08 and AMP's from the '10 era. All are still running strong. The CA's are thirsty, but those AMP's just eat my batteries alive lol. But, I have no problem carrying spare lipos on me. Only a mild inconvenience for me personally.

Anyone else have input on specific motors to look at? Post em up. Can be a help to OP and anyone ever reading this thread
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#11
Nox

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I'm only including motors that can be bought brand new in this as the only old ones that i know any information worth noting about are the Systema Magnums.

 

High priced: StarWei, Action Army, ASG Ultimate

 

Mid priced: Guarder Infinite Torque, Matrix 3000, JG Blue (Gold Eagle)

 

Low priced: SHS High Torque, ZCI High Torque, posssiibly the new Element motors?

 

These seem to pretty much be the only motors worth getting nowadays. StarWei is considered to be "the best," which they technically are, but it's mainly hype around the fact that Umbrella Armory uses them. The build quality is extremely high, the pinions are solid, and they are slightly more electrically efficient than the other two. Action Army motors are generally considered to give the same performance to 99.9% of players, however they feature a plastic endbell. Some people consider this a plus as there is less potential for an electrical short and you can mod them for bullet connectors easier. The ASG Ultimates are the cheapest of these three but still perform quite well. I personally have used them and recommend them over the other two simply because i feel the price difference doesn't really warrant the small performance differences for the majority of players. Unfortunately they don't have a bearing in the shaft like the other two motors.

 

The mid priced motors are kind of a gray area. They are better than the SHS and ZCIs, but not as good as the top three. The Guarders can be kind of hard to find, but they are worth the price. I use a six year old one in my relatively low stress DSG and it gets the job done easily. The Matrix and JG have very strong magnets and can pull a lot. I think both are around 22TPA or so, and the Guarder is 18TPA. I say they're a gray area cause i don't really know where to recommend these lol. I guess if you are doing a lot of internal upgrading but don't care about getting every ounce out of your set up and would rather just save some money.

 

Lastly, the SHS and ZCIs are good if you want a high torque motor on a budget build. I have had some issues with ZCI long types being made slightly too long and not giving much room for motor height adjustment, but the short types have been fine. I use these motors for builds that i plan to use as loaners/back ups, or when it's a gun that just doesn't really need to have a lot of money put into (i.e. a fun gun or one that's gonna be sold). Not to say these motors are bad and won't perform well, but you'll get much better quality control and efficiency with one of the above mentioned motors. As for the Elements, there still isn't much info on these. From what i've gathered they seem to be similar to the SHS and ZCIs.

 

From the list above, i really only recommend high torque models as the increase in trigger response and electrical efficiency is just much more beneficial than a higher RoF. However, the high end motors offered in balanced or high speed models are actually built well enough that you can use them (to an extent) with higher stress builds. I've seen a few posts on the Airsoft Mechanics FB group where people have used 16TPAs and even 14TPAs in DSGs to get incredibly fast fire rates. But all of that science is a topic for another discussion lol.


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#12
TotalNick41

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I'm only including motors that can be bought brand new in this as the only old ones that i know any information worth noting about are the Systema Magnums.
 
High priced: StarWei, Action Army, ASG Ultimate
 
Mid priced: Guarder Infinite Torque, Matrix 3000, JG Blue (Gold Eagle)
 
Low priced: SHS High Torque, ZCI High Torque, posssiibly the new Element motors?
 
These seem to pretty much be the only motors worth getting nowadays. StarWei is considered to be "the best," which they technically are, but it's mainly hype around the fact that Umbrella Armory uses them. The build quality is extremely high, the pinions are solid, and they are slightly more electrically efficient than the other two. Action Army motors are generally considered to give the same performance to 99.9% of players, however they feature a plastic endbell. Some people consider this a plus as there is less potential for an electrical short and you can mod them for bullet connectors easier. The ASG Ultimates are the cheapest of these three but still perform quite well. I personally have used them and recommend them over the other two simply because i feel the price difference doesn't really warrant the small performance differences for the majority of players. Unfortunately they don't have a bearing in the shaft like the other two motors.
 
The mid priced motors are kind of a gray area. They are better than the SHS and ZCIs, but not as good as the top three. The Guarders can be kind of hard to find, but they are worth the price. I use a six year old one in my relatively low stress DSG and it gets the job done easily. The Matrix and JG have very strong magnets and can pull a lot. I think both are around 22TPA or so, and the Guarder is 18TPA. I say they're a gray area cause i don't really know where to recommend these lol. I guess if you are doing a lot of internal upgrading but don't care about getting every ounce out of your set up and would rather just save some money.
 
Lastly, the SHS and ZCIs are good if you want a high torque motor on a budget build. I have had some issues with ZCI long types being made slightly too long and not giving much room for motor height adjustment, but the short types have been fine. I use these motors for builds that i plan to use as loaners/back ups, or when it's a gun that just doesn't really need to have a lot of money put into (i.e. a fun gun or one that's gonna be sold). Not to say these motors are bad and won't perform well, but you'll get much better quality control and efficiency with one of the above mentioned motors. As for the Elements, there still isn't much info on these. From what i've gathered they seem to be similar to the SHS and ZCIs.
 
From the list above, i really only recommend high torque models as the increase in trigger response and electrical efficiency is just much more beneficial than a higher RoF. However, the high end motors offered in balanced or high speed models are actually built well enough that you can use them (to an extent) with higher stress builds. I've seen a few posts on the Airsoft Mechanics FB group where people have used 16TPAs and even 14TPAs in DSGs to get incredibly fast fire rates. But all of that science is a topic for another discussion lol.


Thank you for the write up! So from what everyone has recommended so far I feel like these are the things I'd need to upgrade on the gun; spring, barrel, motor, mosfet, new shell, piston, cylinder, ceramic bushings, sorbo, buckings, and some sort of hop up unit. Please correct me if there anything I missed/wouldn't need/products you would recommend. Thank you in advance.
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