HELP: New 20" Sabre rifle + JP adjustable gas block = short stroki

[Tuukka]

Hi,

New 20" Sabre Defence rifle.

Have changed over: YHM customizable tube, KAC semiauto trigger and JP adjustable gas block.

The JP gas block was used on my previous 20" Bushmaster rifle without issues.

I have tried the JP recommended 0.025" gap between the barrel shoulder and gas block and pretty much also in between 0.012" up to 0.045".

The issue is short stroking and I have also tried the full adjustment range of the screw.

The JP manual does mention that there is a lot of friction in a new carrier / bolt, could this just be a breaking in period? I believe the rifle now has c. 150 rounds through it.

Gas port size is c. 0.095" or 2.4 mm.

Ammo tried have been S&B M193 55gr and Lapua 55gr FMJ, both have functioned without issues in my earlier Bushmaster.

I have sent JP e-mail with regards to this.

[GentlemanJim]

I would suspect gas leakage..from under the block, or around the gas tube

Jim

[patrickbeijer]

Iff you change the gasblock you also removed the gastube.

Iff you put on a gastube that has been used its sometimes worn on 1 side more then the other and this can give leakage.

[Tuukka]

Iff you change the gasblock you also removed the gastube.

Iff you put on a gastube that has been used its sometimes worn on 1 side more then the other and this can give leakage.

Hi Patrick,

I put the new gas tube back with the JP block.

[benny hill]

Open the gas block wide open & add lots of oil inside the carrier.

[CraigS.]

Another possibility could be gas block and port misalignment ,

which in effect could be restricting the gas pressure and cause this problem.

Edited June 8, 2010 by CraigS.

[bigbrowndog]

did you loktite the gasblock on when you put it on the new rifle? I'm with Jim, on this one the only short stroke issue I ever had was due to leakage from the block/barrel interface.

trapr

[Tuukka]

Another possibility could be gas block and port misalignment ,

which in effect could be restricting the gas pressure and cause this problem.

Gas block placement has been checked with an endoscope

Rifle was not shot in original confguration.

Carrier does not bind with the gas tube.

I will shoot it today with my old, well shot in, carrier and bolt. That was the suggestion from JP as well.

Now, if it does not work then, I believe it might only be leak from the gas tube / gas block area. We had one guy with a problem like this, after plugging the leak, his issues went away.

[Tuukka]

Put in the older BM bolt carrier & Colt bolt combo = worked like a charm with S&B 55gr, Lapua 55gr and Barnaul 62gr..

[patrickbeijer]

Do you happen to have the McFarland gasring on the new bolt ? (the one that gave the problems)

[Tuukka]

No, just the standard 3 piece.

I think it is just a matter of breaking in the new bolt carrier & bolt.