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Barrel Length vs Performance

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#1 spazmatic



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Posted 18 July 2012 - 06:40 AM

Like everyone else, I cant wait for the AK series to hit the market.  That being said, the website lists the inner barrel lengths of the two models as:

AKG 74M:    420mm
AKG 74SU:  240mm

I know that this is one of those things that has been debated to death on the internet, but with so much conflicting reports, could someone from KWA comment on if one could "theoretically" expect a more accurate shot/increased range from the 74M compared to the 74SU and if so, roughly how much is barrel length a factor?


#2 aaps59



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Posted 18 July 2012 - 08:16 AM

Im not from KWA, but if the the inner barrel of the 74SU is that much shorter than the 74M, you may notice quite a difference in range and or accuracy. By how much exactly? Thats a question I can't answer. But the tighter and longer a inner barrel is, does affect how the BB travels, especially with gas guns.

#3 greatwatermelon


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Posted 18 July 2012 - 11:52 AM

The idea of a perfect barrel length and diameter is debated all the time, but what is a known fact, even outside of airsoft in the science field, is that an air flow through a pipe/barrel, at some point, peaks at a velocity and stops accelerating further, even when there is still a pressure difference, that is the driving force.

I agree too that this question is difficult to give an exact "theoretical" answer. Just like aaps said, GBB's are different (from AEGs). GBBR's has a continual expansion of gas as the propellant vaporizes, while an AEG relies on compressing the air. The way the gas expands in a GBBR is certainly different when you look at it in fluids point of view, so you cannot simply look at an AEG and say it's the same for gas.

For KWA SMG's like the KMP9, barrel lengths can play a big difference, because the KMP9 is tuned for a very short barrel. When you put a M4 length barrel on the KMP9, you will be firing 600 fps+. Opposed to AEGs, they increase at the most of two digits, maybe low 100 if the difference is huge. (MP5K vs. M16)

The AKG at their lengths will be tuned for 400 fps at their given lengths, so both should have the same fps, just different barrel lengths.

If you look at kinematics only, both have the punch to shoot the same range. But, if you look at how fluids are affected for a longer barrel vs. a short barrel, perhaps its arguable that the longer barrel gives better consistency. If the longer barrel gives more consistency, for a longer range, then the AKG-74 would have more EFFECTIVE range.

I haven't used enough gas rifles to really know if the barre length is a huge difference (if fps is same for short or long) but I could see it noticeably help. On AEG's, I have not seen a big enough difference to care.

To me, I find a person's preference on the length of the gun to be more important than how much the barrel length is going to help out on. Unless your Airsoft games are just shooting far away from each other for few hours.

#4 Tiger_Stripe



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Posted 19 July 2012 - 11:57 AM

Hey guys, long time lurker, thought I'd share my thoughts while we wait for those beautiful AKs.

(Also not from KWA) From my experience in GBB and GBBRs barrel length is a small factor. It only really becomes significant if you cannot alter the flow rate, volume of gas or pressure of the gas used to fire the BB. The best example I can think of for this in the non-GBB MK1, it has a set pressure within the magazine (yes it can change, but I am referring to the lack of a regulator) for the gas, a set flow rate within the hop up assembly, and the hammer delivers roughly the same volume each time. There is however, an upgrade kit that changes the barrel.

The MK1 (back when I had one) is set to fire a bit over 440 fps with a .20g BB. The kit to change the pistol into the MK2 carbine, internally, only changes the barrel length. The MK2 (which I have and love) fires over 500 fps with a .20g BB. I believe that the increase in fps is caused because the MK1 and MK2 expel the same volume of gas, but the MK2's longer barrel uses more of the gas, while the MK1 inefficiently expels it out the end and cannot impart any more energy to the BB.

This is also seen in Classic airsoft guns, where it is know that reducing the bore size (6.05mm to 6.03mm etc.) will more efficiently use the expelled gas (more fps), and increasing the length of the barrel will increase the fps up to a peak where any more length will become detrimental (since it would throw off the ratio of the volume of expelled gas, to the volume of barrel and kick it out of the 1.5:1, volume:barrel volume, or 1:1 sweet spot).

Sorry I don't have anything tested or concrete, but that's, my two cents on barrel length. We'll have to experiment when these hit the shelves, I can't wait!

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