Overgassed AR-10 JP gas block problem

[jeremyro]

I have a Fulton M110 clone rifle and it was pretty overgassed when I got it with the standard gas block and rifle length standard weight buffer system. I was getting swipes and flattened primes even with pretty light loads and so I got a JP adjustable gas block to try to improve things. I swapped them and started testing as specified in the manual. I got the adjustment screw backed out all the way and it was still not locking back. It would eject a round but never lock back no matter how open I made it. I tried cycling two rounds and it short stroked and ftf the second round. I am not sure what I am doing wrong here. I reused the old gas tube and the block seems to be centered. It is not setup for a handguard retainer and the old gas block was flush. I was running 178gr amax with 42 and 43 grains of varget and neither would lock back. Primers looked much better though.

[nate76239]

Wow so you started with the screw closed and never got the rifle to lock on an empty mag, did you try any factory ammo? I have a Wilson combat gb and i adjusted it with 147-150 grain fmj ammo afterwards i used 168 grain ammo but didn't adjust the gas block.

[KaLiFORNIA]

Sounds under gassed

[FeuerFrei]

Maybe the loads are too light.

Rifle is already broken in with full power factory ball?
Rifle has no custom action spring/buffer installed?
Using known good mags?
Reset gb adjust screw and use OEM weighted action spring/buffer and shoot full power ammo to test.
Test ammo in another AR10 clone if possible.

[scotty99]

[triggs75]

Have you tried loosening your gas block again and try re-aligning it. Maybe wasn’t lined up correctly the first time.

If I’m reading it correctly - you were over gassed so you swapped gas blocks and now seems under gassed.

[damon1272]

Triggs is most likely right. You are not lined up properly on you gas hole. It is easy to do with the JP clamp on gas block....ask me how I know...

[jeremyro]

After reading some responses I took it apart and you can kind of see the imprint of the old gas block that was lined up and the new one that was too far forward and slightly canted. I took some careful measurements and reset it. I will take it out next weekend and see how far I get.

[KaLiFORNIA]

It'll work now!

[jeremyro]

It'll work now!

I hope so! The brass was looking so much better. I would like to be able to load this to some decent pressures. I dont think anyone has ever accused lightly loaded 308 of being a great long range cartridge.