TucsonAirsoftCoalition.com

Refer to this text:
http://www.airsoftsociety.com/forums/f3 ... #post14674

"Putting a 500mm long barrel in a gun with a cylinder designed for a 363mm barrel is looking for trouble. Your cylinder will not have the sufficient air volume to propel the projectile down the entire length of the barrel. "

also in the text it said:
"Test Bed #2 (Long barrel, High FPS, Moderate ROF):
Inner Barrel Length : 600mm (600mm X 0.03937 = 23.622 in, but let’s call it 24”)
FPS: 400 (the golden number for many)
Cyclic Rate: 15 RPS
Calculations:
At 400 FPS, it takes a BB 0.005 seconds to travel 2 feet (24”, or just over 600mm).
[1 second, divided by 400 feet, times 2 feet]
At 15 RPS, a BB is fired once every .066 seconds.
[1 second divided by 15]
At Zero Point (piston release), the BB exits the barrel at approximately 0.005 seconds, leaving 0.061 seconds before the next shot even begins to travel down the barrel.
[0.066 minus 0.005]
The BB is only in the barrel for the first 7.5% of the firing cycle."

so my question is, am i going to have "trouble" if I put a (M16)509mm inner barrel in my KWA M4 that has 400+ fps with .2's?

I ask this because in the equation, with the 400 fps the bb was only in the barrel for 7.5% of the time. so with this, i doesnt really matter how long the barrel is because with 400 FPS the bb is going to be long gone before the cylinder starts to retract..? right?

(and i do use .25's btw. so my FPS is around 380.)

It wont have any problem. I put a 509mm barrel in my KWA, no fps decrease or anything.

mahabra695 wrote:It wont have any problem. I put a 509mm barrel in my KWA, no fps decrease or anything.

then i guess the question is, did it do anything positive? or was it the same.

Well, it obviously made my gun more accurate. If you call a 7fps increase great, than ya.

I'll just toss some recent experience in.
2 different guns, 3 different barrels.
590MM 6.01
509MM 6.XX
500MM 6.XX

VFC Stock M16
DBoy AK

All tests made with .25 ammo

VFC+509MM = 'Accurate' to 70-80M. 8-14" Spread at 50M
Dboy+500MM = 'Accurate' to 60-80M. 12-20" Spread at 50M
VFC+590MM = 'Accurate' to 30M. Unable to (effectively) reach 50M
DBoy+590MM = 'Accurate' to 80+M. 4-8" Spread at 50M

So, my experience says that your standard V2 M4/16 gearbox will have no trouble with anything up to a 509MM barrel. However, that seems to be your max; even a small extension past that is gonna bone you.
But: the V3 gearbox in the AK appears to push enough air to manage the 590MM barrel.

I'm going to preform a more controlled test tomorrow, instead of randomly mixing hopup gear.

i see, but the V2 M4 and V2 M16 gearboxes are different in that the M4 does not have a full-cylinder and the M16 does have a full-cylinder. yes?

They should be the exact same. I see no reason why the factories would pay extra money to make/bring in a specialized part.

because on the m16's they have a stock 509m inner barrel. m4's have a shorter inner barrel.

If you're going to use a 509, make sure you have a full cylinder. Sometimes m4's have full cylinders, and sometimes they have ported ones.

at no point in rof is barrel length going to be your limiting factor... don't worry about that math, it's completely erroneous anyways. BB doesn't accelerate to 400fps instantly, and starts before the piston finishes it's travel... so there's way too much unaccounted for there.

going past a 400 or 450 won't significantly increase your accuracy at 400fps, assuming the barrels are of equivalent quality. Higher quality barrels are much, much more important than longer barrels.


Savage:
Unless your AK has a bore-up kit, or your VFC has a ported cylinder... then they both have the same volume of air being pushed from the gearbox. Ver2 and Ver3 cylinders and stroke lengths are the same.