Why has my fps increased

[Beef]

Ok guys bare with me this is a bit long winded.

Basically i bought a G&P Zombie killer shorty which was firing at 328 FPS. I decided to change the front to a full length m16 front end. When i did this the FPS jumped upto 400+ FPS. I was told by a tecky that this was due to the longer barrel etc as when it originally was short the piston was high powered to provide 328 fps out of such a short barrel or the spring was powerful, something like that.

Anyway so after a spring change it went down to 345 - 350 FPS. this was over a year ago and i hardly use this m16.

Anyway recently i changed the hop rubber and cronoed it at 320 fps. I checked the inner barrel and saw that the copper ring that goes over the inner barrel and forms a seal into the hop was loose so i taped it in position so stop it coming loose and to form a decent air seal and then when i cronoed it it was doing 380 FPS.

What the ehll is going on??

[JOE90]

Re: Why has my fps increased

as you said yourself, you tried creating a better airseal and you have done so, cylinders and barrels need matching, ie ported cylinders and non ported need to be matched with the correct length barrel so you dont loose/gain fps, just remove your tape mod and it will go down again

[Beef]

Re: Why has my fps increased

If i remove the tape the copper circle thingy will slide down the inner barrel?

[JOE90]

Re: Why has my fps increased

thats for stabilty aswell as a bit of airseal, put the tape in front of it so it cant slide down rather than on and over it creating a tight seal

[Beef]

Re: Why has my fps increased

did that and fps dropped to 360

[Caveira]

Re: Why has my fps increased

To be honest, I've lost those rings so often and never noticed the difference that I think stability is far more of an issue than air seal. I think the tape provided the increase, not the ring itself.

Another thing that will increase fps is gearbox efficiency. If you've re-lubed the box while changing the spring that will make things move that little bit quicker. Put simply, if there's less resistance in the box the piston can move faster and if the piston moves faster then the fps goes up. A good example is that one of the northern shops found they had to use cut-down m90 (from memory) springs to keep new G&G (again from memory) standard AEGs under 350 as the boxes are so mechanically efficient.

[JOE90]

Re: Why has my fps increased

did that and fps dropped to 360

Now adjust you hop on if its not already, you said yourself you havent used it for a while, get a few thousand rounds through it, let things settle a bit, as robin said, the rings not essential as ive lost some also, but just keeps the barrel that bit more stable. After a bit of a wear in it should drop a tad to 350 if your lucky if not then spring change it is again lol

[ElCarl]

Re: Why has my fps increased

A good example is that one of the northern shops found they had to use cut-down m90 (from memory) springs to keep new G&G (again from memory) standard AEGs under 350 as the boxes are so mechanically efficient.

iirc it was cut down M80 for a KWA
But either demonstrates it pretty well

[seansamurai1]

Re: Why has my fps increased

It's also the long barrel, going from a short barrel to a long barrel effects the FPS. The BB has longer time in the barrel to accelerate!

[HunterAndy]

Re: Why has my fps increased

In that case only if the original barrel was not optimally matched to the cylinder- in the case of the cylinder being either unported or ported too far nearer the spring guide end for the barrel.

[bill1310]

Re: Why has my fps increased

well thats all my questions answered without doing a thread thanks guys

[Beef]

Re: Why has my fps increased

In that case only if the original barrel was not optimally matched to the cylinder- in the case of the cylinder being either unported or ported too far nearer the spring guide end for the barrel.

What cylinder does the stubby use as i kept the gearbox orginal apart from changing the spring to bring the power down from the 400 fps+ down to 350.

I dont want to have to change the spring again as i did that last year .

[JOE90]

Re: Why has my fps increased

you need a ported cylinder

[Beef]

Re: Why has my fps increased

what's the difference/benefits >>

[johnnyj]

Re: Why has my fps increased

G&P dont use ported cylinders there a sealed unit thats been in there 7mm and 8mm now for many years on all guns (rifle/stubby bar these cheap sportline type 7mm gb's) , the standard spring in g&p guns should be a little over 360fps new i would say use a 1j or m90 spring to bring the fps down