firing ok but only 190 FPS

[TopSillySteve]

hello guys

i have built an AR-15 from spare parts looks like its getting distance but when i tested the fps it only gets 190ish ive been told its either the spring or a hop issues

can anyone think which one i need thing is i need it for sundays game at the mall any ideas guys ?

[johnnyj]

Re: firing ok but only 190 FPS

It can be a number of issues sorry to say , when you built it up did you test the piston for resistance when pushed in the cylinder ? are all the parts new ? what rated spring have you used ?

[helpimonfire]

Re: firing ok but only 190 FPS

Might be a silly question, but if you say you're getting the distance but low fps... Are you using .2g's to chrono? Heavier rounds will drop the fps substantially if you're running .28's or even .3's.

[happyal]

Re: firing ok but only 190 FPS

If you are getting the distance I wouldn't worry too much about it.

If you really are worried about it and what to get to the bottom of it, I would start at the hop unit and work backwards.

Check the hop rubber seal with the barrel, perhaps use some telfon tape, next the hop unit seal with the gearbox. Next comes opening the gearbox, Check the O ring on the piston head, might as well change the spring if you have any doubts with it, check the cylinder head and give everything a good lube to ensure smooth running.

That's the basics that I woudl start with.