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G&g Gc16 Predator Barrel/hop-Up

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I'm currently in the market for a barrel & hop-up upgrade to my G&G GC16 Predator. The predator comes with a 260mm 6.03 brass barrel. The rifle shoots around 335 fps stock.


Goal: Create a second barrel setp-up that can be quickly swapped with my stock internals for outdoor play. I would like to raise my FPS to at least 350. 


My current contenders are as follows...



300MM Prometheus 6.03

300MM PDI 6.05


For outdoor play, I plan to use a mock suppressor to hide the longer barrel. For indoor use, I plan to use the stock barrel and hop-up unit because it seems fairly consistent at <50ft.  My  concern is that the 6.05 PDI would not increase my FPS due to the wider bore. Thoughts? I have heard great things about the PDI and Prometheus and most sites sell the two barrels mentioned above for a similar price. What FPS increase could/should I expect out of the same bore but 40mm longer? Should I expect any compression issues with a 40mm longer barrel or is this within the stock system's limits?






I currently use a ProWin in my CA M4 and it feeds perfectly; however, when I tried it in my G&G, it would not consistently feed my K-120's. I realize this may have more to do with the gun's magwell but I wonder if the Retro-Arms would possibly reach further into the magwell and feed more effectively. Has anyone had experience with the Retro-Arms M4 hop-up?  I have also read concerns over the "new" ProWins and that they may no longer be made as well as the previous generation. 




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As far as barrel brand, both you listed are good. Prommy still effectively holds the top spot in comparison from my end, but thats not to say it is better, its just preferred from working with them forever now. With a good bucking and good air seal, you'll get great results with a Prommy Stainless Steel barrel.


Although yes a tight bore can increase FPS, it doesn't do so by much, and at max you might get an extra 10-15fps, depending. However, this is assuming an upgrade from a standard 6.05-6.06 stock barrel into a 6.03 tight bore. If you already have a 6.03, then neither of these barrels are going to cause any noticeable effect to your fps. Now it you upped it to a 6.01, then yes, you would see the 10-15 fps increase, but then you move into a new realm of having to religiously maintain and clean that barrel because if it jams, you won't have a prayer of getting it un-jammed.


If you go with the 6.05, then you will notice a slight decrease in fps from your current setup. 


When you begin to talk about longer barrels and compression, particular changes do come into effect. Ill keep it short and simple. The volume of the cylinder to volume of the barrel requires a particular ratio. A standard M4 comes set with the correct ratio (typically) and this is controlled by the location of the port on the cylinder. When you begin to alter barrel length, you need to correspondingly alter cylinder port location. Why? Well, if the volume ratio of the two gets too low, then there isn't enough pressure to push the bb out of the barrel effectively (example is keeping the cylinder, but making the barrel longer). If the ratio gets too high (keeping the cylinder, and shortening the barrel) then once the bb leaves the end of the barrel there is still a large buildup of pressure behind the bb that is still expanding outward at a greater speed than the bb. This additional expansion can cause alterations to the flight path of the bb, effectively causing detriment to the accuracy of the gun. What you want is the sweet spot, somewhere right in the middle. However, there is no good way to determine the sweet spot, so we use a range for the ratio to remain within. The rule of thumb is that it is better for the ratio to be higher than lower, as lower ratio with lower pressure ultimately effects the bb more significantly. There is no true answer to this ratio, but there is a desired range for that ratio to be, aka somewhere within 1.5-2.5 for standard barrels. For longer barrels, the typical ratio is between 2 and 3. Make sense?


Now, if you are talking about a difference of only 40mm, that translates to only ~1.6 inches, which is not much at all. Because the ratio is a range rather than a value, for that short little increase, there are probably not going to be any significantly noticeable effects (i.e. you are probably fine with the current cylinder). You loose overall "efficiency" from an engineering standpoint, but the point im getting at is that when you pull the trigger, it will fire the bb fine, and with the naked eye, you aren't going to notice any true detriment. If you were to up the length by 100mm though, thats a different story.



As far as hopup, the Retro-arms are relatively new. Prowin has been fantastic in the past, but if you are having feeding issues, it might pay to look into the Retro-arms or another brand hopup. Sadly, there is no set answer for an issue like this (tolerancing differences are a pain); it is typically solved by a trial and error process.


Hope this helps

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