Longer barrel on an M4?

[impi]

My A&K LR300 is basically an M4 with a folding stock. I bought it in Korea with a KPS approved spring installed ( so I'm assuming sub-300 fps ).

I have an AK inner barrel that I'd like to insert into this gun. Longer barrels are supposed to improve accuracy and increase fps.
The barrel is about 55cm long ( not too sure since I don't have my ruler here now ). The original barrel was 34cm long.

Will this barrel be too long for the current setup?

I know that if your cylinder to barrel ratio is too much ( meaning the barrel holds more air than the cylinder ) it will actually slow down my fps since the cylinder will have run out of volume before the bb has left the barrel. The bb will then start to slow down since the driving force behind it has been spent already.

Any advice? :confused:

[krobinson103]

Only happens if you have a really stupid rate of fire. No one is using that sort of modded gun as far as I know. 55cm is about the length of the barrel in my sig 550 and it works fine. I don't run anything over 8.4v but even then I have no complaints.
When you get down to the math 300fps is fast enough that even with a high rate of fire the bb will clear the barrel before the next is ready.

[piloth]

In my opinion, NO.

I Have a lab data about the barrel length, from Japan. M4 barrel is enough to enjoy airsoft. No data support that longer barrel than m4 makes your gun more accurate.Trust me.

And bassically, chaning inner barrel into loner one without changing outter barrel compatable with it , the end of innert barreal moves more than shoter one when you shoot. Asseum that at the end of outter barrel, inner barrel moves 0.1mm. If the inner barrel ends with outter berrel , inner barrel just moves 0.1mm but if the inner is longer than outer, the more lengh the more move at the end of inner barrel.

I let you know one thing. M4 Hop up system was desinated 20years ago and has born problem you can't fix. G36 and M14 have more improved hop up system and have more accuracy and more range. Data from Japan says like that. There is a way to fix M4 Hop up system but it's a little bit hard. So I recommand to use other gun than M4 or M16 or anything else with M4 Hop up system. G36C has shoter barrel but more accuarate then M4. Shooting rage is better as well.

[Righteous]

You'll have to open the gun and look at the gearbox to see the cylinder. Check for holes (ports) in the cylinder. If it has them then getting a longer barrel probably won't help. If it has no ports then you should be OK, but 550 may be too long either way. I looked at some LR 300 cylinder pictures on line and they did not have ports. There is a long barrel version of the gun so A&K probably uses the same internals for both to save costs. I also looked up the TM AK47 barrel length and I found a value of 455mm for it. Based upon this you should be OK for the longer barrel but you will need a fake suppressor or similar item to cover the end of the inner barrel. A tightbore may not help since the volume isn't much different from standard bores.
Here's some math to help: Standard bore = 6.08mm internal diameter, M4 barrel = 340mm length, Volume = 9871 cubic mm. For a 550mm barrel the volume is 15968 cubic mm. Your cylinder to barrel volume ratio should be at least 1:1 and more like 1.5:1. You'll have to measure the length and internal diameter of your cylinder to get these numbers. Keep in mind that an M16A2 barrel is about 509mm and M16A2 cylinders are longer than M4 cylinders. I bet your AK47 cylinder is longer than your LR 300 cylinder. Also, porting reduces the amount of air that goes out the nozzle to propel the bb as some gets pushed out the side of your gearbox and I don't know how to calculate that but I believe it is based upon the shap on the ports as some are more cylindrical and some are teardrop shaped. Don't bother with bore up kits as the small increases in diameter don't help much especially given the cost.