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Does longer barrel increase accuracy?


Raphiki

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I got a little feisty on another forum earlier about this topic. So I did a little searching around and talking to people.

 

Q: Does longer barrel increase accuracy?

 

Raphiki's Short Answer: The difference between a 363mm to a 407mm inner barrel in either scenario is likely not to be truly noticeable by the average player; more of a feel good "I think, therefore it is" mental thing. The actual difference is an elitist debate.

 

Because I got a little feisty and couldn't let a dead horse lie, I decided to look up what I could on the topic. I found an outstanding post that I want to share with you.

 

Source: Airsoft Forum, user "xlizer"

 

Here is the long answer:

 

I have done a fluid mechanical approximation of the airflow through a barrel blocked by a BB. It seems to suggest what I would say is the most sensible solution: Increasing barrel length yields exponentially decaying greater accuracy.

 

Allow me to summarize:

 

Airflow from the gearbox is turbulent. Airflow from the nozzle propels the BB forward with a very high force parallel to the barrel (henceforth referred to as the Z direction), and a smaller force perpendicular to the length of the barrel (henceforth referred to as the perpendicular vector) in a random direction. Additionally, there is a swirling effect caused by the turbulent flow that causes more smaller random forces which can be approximated as a torque.

 

Setting the direction of the barrel to be the Z axis, hop up causes the BBs to spin counterclockwise about the Y axis. This imparts an angular momentum which resists the smaller torquing forces by a gyroscopic effect. Hop up does not create a force in the positive X direction while the BB is inside the barrel. This is because the "Lift" is caused by the Magnus effect. Inside the barrel, fluid is pushing the BB and escaping around the edges. The Magnus effect cannot manifest under these conditions because it relies on the spinning projectile passing through the surrounding medium and pulling a pocket of fluid along with it. While the BB is in the barrel, though, there is still "lift", but this is due to a similar and nearly opposite reason.

 

Let us imagine a BB being propelled by non-turbulent flow perfectly parallel to the Z axis without touching any barrel surface and having a counterclockwise spin in the Y axis. Bernoulli's principle would have more pressure exerted on the bottom of the BB than on the top because fluid is traveling with a lower speed relative to the surface of the BB on the negative X side and higher speed relative to the surface of the BB on the positive X side. This creates a pressure differential which exerts a force in the positive X direction. Any other force vectors will cancel out exactly. For the case of turbulent flow, they will not cancel out exactly, and will create a slight wobble in the path of the BB. Due to the (relative to the torquing force) overwhelming force in the positive X direction, the BB will be guided by the potential energy well caused by the upper surface of the barrel.

 

As the BB proceeds down the barrel, It will actually increase the hop effect due to friction against the barrel and the flow of fluid through the gap on the underside (Negative X side) of the BB. This will increase the damping of the torquing forces to a small (probably negligible) extent. As the BB gets further from the barrel, the turbulent flow will subside somewhat, which means the torquing forces will also diminish to some extent. This will cause the BB to be further stabilized by the aforementioned potential energy well.

 

This potential energy well is also what damps the original force along the perpendicular vector. This particular force will die out, and can be modeled by after a simple differential equation.

 

For an over-simplified visualization of this process, imagine a marble rolling down a semi-cylindrical track wider than the marble. If the marble is placed off-center, it will roll down the track while its perpendicular vector acts like an underdamped oscillator, which approaches zero amplitude.

 

As the BB leaves the barrel, there is an area with greater turbulent flow. This is where the crowning at the end of the barrel becomes important. Very good uniform crowning will cause less interference with the path of the BB, and poor, inconsistent, or missing crowning can cause air currents to blow the BB off-path. Once the BB is free of the propelling fluid and into the atmosphere, the Magnus effect takes hold and creates the lift we describe as hop up.

 

A longer barrel should therefore allow more time for the BB to settle into the potential energy well, which in turn causes greater consistency, and therefore greater precision. The gains to precision, however, will be exponentially decaying as the barrel length increases.

 

All the preceding is assuming a properly matched propellant source and barrel length. If the propellant airflow stops while the BB is still in the barrel, then the BB will have to move through the air in the barrel, causing the "Lift" to switch sharply from the positive X direction to the negative X direction. This, coupled with extremely turbulent airflow could cause the BB to bounce around the barrel before leaving it, decreasing consistency.

 

This does not provide a practical answer to the question at hand, as I have not solved for the point at which diminishing returns make increasing barrel length not a practical way to increase precision. Also note that this assumes a fixed reference frame (eg. barrel). Bear in mind that this must be coupled with the shooter being steady, as any vibration or motion of the barrel as the BB is still traveling through it will cause undesirable effects, and that the body and barrel of the gun is stable enough to not allow vibrations from the gearbox/piston/gas chamber to move the barrel enough to cause similar issues. There are more factors at hand than barrel length. This is only addressing the case of perfect shooter and gun body. If the shooter is less than stable, a shorter barrel may be more accurate than a longer one since the shooter will have less time to disrupt the BB flight path inside the barrel.

 

In summary, a longer barrel will provide a more accurate shot and consistent groupings given an adequate shooter. Realistically though, there are many more important factors than barrel length. Hop-up is the most important factor for accuracy and consistency. Other factors are barrel bore and quality (Let's face it, most stock barrels are very good, though it would be impossible to have accuracy and consistency with a deformed barrel.) as well as shooter stability and gun build quality.

 

EDIT: Actually, let me answer your actual question. I have an ICS L85, and I've never seen the internals of the Army one, so I'm going to answer this in terms of this gun. Given ideal conditions, I believe that an L85 should have superior accuracy to an M4. First of all, the hop-up unit on the L85 I have experience with is far superior to an M4 hop in terms of stability. Furthermore, the barrel/hop unit is anchored very well to the body of the gun at 8 points. Also, the L85 is a heavier gun. As such, vibrations from the gearbox would create smaller amplitude vibrations in the barrel than those in the M4, which would throw off consistency.

 

On the topic of vibrations in the barrel, I also firmly believe that low amplitude high-frequency vibrations (like those from the gearbox) are worse for consistency than the high amplitude low-frequency vibrations from a human shooter provided that the latter does not effects the point of aim. This is, of course, simply from looking at the ballistics. The fact of the matter is that swaying of the shooter effects the point of aim, and mechanical vibrations do not, so the perceived effect of the swaying would be greater.

 

As a final disclaimer, This is mostly an academic exercise. In practical terms, the difference in accuracy isn't very appreciable unless you're one of those types who try to go for the most technically ideal system. I refer here to the obsessives who feel compelled to get every possible bit of range and consistency out of their guns in the hopes that the combined effects are appreciable (in some cases they are 400' effective range currently in progress towards 500'). I think that this does not apply to you, however, since you're looking at an Army L85. The Army is plagued with the design flaws of the early G&G L85 (as it's a clone), and also introduces QC issues (again, as it's a clone). They're not impossible to correct if you're comfortable with mucking around, but I've seen some truly unpredictable faults with them. Specifically, a friend of mine managed to jam the safety in the safe position, rendering it inoperable. He further trashed it while trying to fix it, though I can't speak for his mechanical aptitude.

 

I think you'll be better off with the G&G. You'll have to replace many parts of the Army to get it up to the same level.

 

 

This is debate and discussion time. Don't trash this post with unfounded opinions, one liners, or be a troll in general. Please reply if you have valid points to make and or sources to cite.

 

 

 

Edit: Please do not take this discussion off this board without citing your sources.

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Imparting backspin, lift and minimizing variation will do more for accuracy and distance. The longer barrel will allow you to maximize compression and air volume to get full use of the air being pushed by the cylinder which will increase speed. So longer barrel will not have as big of an effect as imparting more backspin to stabilize the BB will on accuracy.

 

Just my 2cents.

 

RD

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I'm with Dave, a longer barrel shouldn't really add that much range, however if you're comparing an Mp5k to a PSG-1 there will be a noticeable difference but if you have a 363 compared to a 409 then no the difference would barely be noticeable if there is any at all. Hopup chambers are the main thing to adding range and accuracy.

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Upgraded with the same internals, I see no difference in range or accuracy between my Spetz and my other full sized AKs. Thats not by any means scientific, but it works for me. I realize some people like to squeeze every ounce of performance out of toys, so more power to them. ^_^

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TL;DR

 

If a symmetrical object is guided along a fixed path longer than not, it will more than likely travel along the path it was projected, was it not traveling in fixed position for the same distance, I.E. half the distance, or a quarter of it.

 

SEE ALSO;

 

ALL AIRSOFT GUNS SHOOT A SPHERICAL PROJECTILE FROM A SMOOTH BORE BARREL.

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  • 2 weeks later...

Theory - Schmeary...

I would lke to see data. Show me a study or do a test with different length barrels at different FPS to find the "effective range."

Theory is just written words and ideas of how things work in a perfect world.

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I liked this explanation, but yet it still requires testing and recording. He mentions that the TW5 seems to shoot farther and straighter than an M4, and by my personal experience, I can say it does seem true. I didnt notice any difference with my M4 PTW vs. M4 CQB PTW, however (with my CQB, I hit a guy at 200 feet at Irene). I wonder if we can get some guys with the SR5 vs. SR10 vs. SR12.

 

Taken from collective posts from Tackleberry of the PTW Euro Forums.

 

At the end of the day we're dealling with musket technology here. Remember a light weight round ball down a smooth barrel is never going to win any awards for pin point accuracy.

 

For best accuracy/range the BB needs to travel down the barrel on a cushion of air without touching the inside.

 

If you make the space between the BB and the barrel too small it will come into contact with the walls of the barrel and this will have a negative affect on the BB's flight path.

 

Think of it like this:

The only point the BB wants to touch in any part of the barrel once propelled forward is the hop bead. After that any contact with the inside will either reduce or increase backspin. This will then cause the BB to fall short or fly upwards more than intended.

 

The other effect is if the BB touches the sides it will cause it to hook left or right.

 

So by making the barrel too tight or too long, you will reduce the accuracy of the fired BB...and not gain any range...only velocity.

 

So the shorter barrel or one with a slightly larger bore will give the best accuracy.

 

Speaking of Systema PTW:

General concensus of opinion is that the ideal barrel length for an AEG is 280mm, and I swear the TW5's (MP5PTW) shoots further and straighter than the M4's/CQB-R's.

 

6.01mm barrels are just a marketing gimick to make you spend more money when you don't need to. The 6.04mm is the ideal size, and therefore the barrel that comes with my PTW, as standard, is perfect for the job.

 

Here are some things that affect range/accuracy:

Make & quality of BB

Ambient temperature

Wind (dosen't take much more than tiny eddy current to mess up that perfect shot)

Cleanliness of the the barrel

Wear & tear on the hop bead

Condition and servicability of the cylinder/piston/nozzle

Dust, grease and other contaminants that get sucked in and blown out with each shot.

 

And the simple fact you are relying on the back spin of the BB to get a decent range....!

 

While we try our best to ensure these things work as well as possible, it's always an uphill struggle against the basic facts.

 

Airsoft replicas work in the complete opposite to the real thing. That is the shorter the barrel the better the accuracy.

 

A good example is to see how far and straight a good marui GBB fires a BB, and that has a barrel no longer than a cigarette.

 

You would only use a longer barrel to gain muzzel velocity, but to be honest the gain will only be small and it's far more important to get an accurate shot.

 

It's also worth taking into account that using a 6.01mm barrel does not make an AEG more accurate. It's primary function is to increase muzzel velocity.

The smaller you make the gap around the BB, the less air escapes past it and thus more thrust is applied.

 

Accuracy/range is always down to the hop up and how well it is maintained and adjusted....not the make of the replica.

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Excellent post, Bishop, maybe one of the best we've ever had.

I agree. Thanks Bishop.

 

 

The 6.04mm is the ideal size

I've been using the KM/Head1950 Tightbores since '05, and I agree. Never had a jam, and still plenty accurate.

I never saw the need for 6.01mm barrels.

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This is not a very scientific post but I have personally removed the stock 263 mm barrel from 2 separate KWA SR5s and replaced them with 363mm 6.03 barrels (one was a JBU and the other was a madbull) The results were more than impressive. Both guns IMHO had a significate range increase and the grouping also seemed to get much better. Rampage is currently using one of these SR5s. It shoots amazingly good and has a 6 inch group (with the occasional flyer) to 175ft or so.

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Plus you gotta clean the 6.01 barrels twice as much as you would have to clean 6.04+ barrels

 

too many downsides

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  • 2 weeks later...

@Zebrex... on that gun what was the FPS change? That would have been the biggest improvement with the longer barrel in the SR5's.

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@Zebrex... on that gun what was the FPS change? That would have been the biggest improvement with the longer barrel in the SR5's.

 

It was significate in both guns. The first one I did with the JBU went from 330s to the 360s and Rampage's gun went from a consistant 347 to a consistant 372.

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