Barrel Length Vs FPS?

[Liam Porter]

What effect does barrel length have on FPS?

Providing everything stays the same/stable apart from barrel length.

My step dad has a G&G GR300L, with a 460mm barrel.

He changed the barrel (inner and outer) to a shorter one, a 180mm one.

His FPS dropped from 330-260. Any ideas why?

This was a direct swap from another gun, whose FPS went from 330-335, so essentially, no change.

The cylinders weren't swapped, so what's happened is:

A cylinder for 460mm barrels is now using a 180mm barrel, and FPS has dropped from 330-260.

A cylinder for 180mm barrels is now using a 460mm barrel, and FPS hasn't changed.

Thanks for any help.

 

[mattswan2512]

HMMMMMMM that is odd normally you need to be carefull about big barrel length increases on full auto due to drag bk from the piston so when the bb would normaly of left the barrel the piston is being pulled bk again under the gears causing drag. this can cause fps drops in MAJOR barrel changes but not when going the other way so thats weird!

Ill have a think and c if i can work out why......

maybe change the piston and cyclinder over for both guns as i think the hole in the cylinders affect when the compression is released!!!

Ive taken apart a few boxes in the past but im no expert

 

[RR01]

I found this happened on my G&G CM16 (229mm inner barrel). The box it came in said it was doing 320 ish but every site chrono and my own said average 275. Whilst doing a gearbox build for someone I tested the standard G&G lower with different lengths of inner barrel in the upper and as the barrel length increased, so did the fps. Using an OE 335mm inner upped the fps to 320 and using a 509mm had it shooting 365. Nothing changed other than the inner barrel length, as I used the same hop unit and rubber on each inner barrel. That helped me set the gearbox build to the fps the customer wanted, based on the inner barrel in the gun it was going in. I've now added a bigger spring in the G&G to get the standard fps up to 320 using a new 6.02mm x 229mm inner barrel. If I put a longer upper on it I suspect it would be very site unfriendly now.

Not sure why your using a shorter barrel on the setup for the longer didn't change, but my guess on the longer in shorter is that the extra length allows the air pressure to build more behind the bb as it has a longer time in the barrel.

 

[TPI]

thats exactly right RR01

Cylinder's are made different some will have porting some won't i can't remember it all at the moment (Ages ago since i last even thought of it) but they will also be lighter and heavyier different materials even! the same goe's for inner barrels Brass - Aluminum Long - Short Tighter - looser (i'll stop their as this is going past PG13 otherwise)