JP Adjustable Gas Block isn't adjusting correctly...HELP!!

[Tedward]

I have a AR-Stoner 24" Grendel B&B with JP lowmass bolt carrier and silent capture buffer spring. The buffer (lower) works fine with my Wylde and Beowulf but I have the problem below with my Grendel Upper.

I am trying to get the gas block adjusted right and having difficulties.

Trying 1 bullet at a time so the bolt will catch and hold back. No success. I have gone from not ejecting to ejecting and not holding back the bolt.

So I used 2 rounds to see if it will strip the second round. It shoots, ejects but doesn't strip the next round. It even sets the trigger.

So is it not traveling far enough to lock back on single shots or enough to strip the second round? I think the bolt isn't traveling back far enough but how can I find out? It locks back when I pull the charging handle so wondering if the hole isn't big enough in the barrel.

Any suggestions?? Oh, also using Wolf Brass ammo. Is that the problem maybe???

[ricsmall]

Pull the gas block and measure the gas port with drill bit. Pretty sure you should have an .0935 port on a 24" pipe. There is a thread on here about port sizing, use the custom search engine, and I'm sure some others will chime in.

[Tedward]

I got it. Really think its the right size hole because Liberty makes the barrels. Also finding if I pull back the charge handle and release with an empty mag, even a P-mag, it slaps up into the barrel extension. Doesn't lock open unless I push the bolt catch up.

I already took the Silent Capture Buffer out of the equation and stuck a rifle length buffer spring and buffer in but no help.

Did that and ran 20 rounds of Hornady 123gr VMAX, no change. I also started from screwed all the way in and then backed out 2 full turns. Each time when it didn't eject increased by 1/2 turn each round as recommended by JP. Did that till it cycled but the bolt never held back. Then tried to run 2 bullets and it never went back far enough to snatch up the second round.

So I'm wondering if it's the low mass carrier. I'm going to use my regular Fail Zero BCG tomorrow, swap out the bolt and see if its the Low Mass Bolt Carrier.Then if it still happens off with the Adjustable gas block, take some measurements and if all looks correct, I'll install a regular gas block. It has to be one of the 4 things. I think I might even try a different lower to eliminate the bolt catch but that still doesn't solve the feeding issue....CRAZZY GRENDEL

[babaganoush]

Tedward,

Have you tried other mags? Just a thought, but not an entirely wild one.

A different lower can also answer a whole fleet of questions.

My FTF issue was resolved when I replaced a tweaked upper, which was bent by over-enthusiasticly tightening a clamshell holder (yes, the pilot was installed in the upper).

David

[CPT.CRAZY]

Is there oil in the buffer tube? I have seen to much oil there cause the same problem. You don't have an extra buffet pad or any thing like that in the gun do you?

[Tedward]

I did try other mags and same issue. Tried a few other things and will be posted next. thanks

[Tedward]

Pull the gas block and measure the gas port with drill bit. Pretty sure you should have an .0935 port on a 24" pipe. There is a thread on here about port sizing, use the custom search engine, and I'm sure some others will chime in.

Well if all fails go the forum for direction and read the directions.

First went to square 1 and removed the JP LM BCG and used my original BCG, full mass, and removed the silent capture buffer and replaced it with a standard buffer and spring. Only difference now is the JP Rifle Adj. GB.

I expected more out of JP Rifles. The main issue was the gas port lining up. I used the rifle with my $45 gas block and it worked fine. So I upgraded to the Adjustable Gas Block to make it work smoother and it sounded like that’s what lots of guy’s do.

When I removed the AGB I measured the hole as recommended by ricsmall. Since the rifle cycled fine with the non adjustable gas block the size shouldn’t have been an issue. Since I don’t have a .0935 measuring tool, I checked the size with the drill bits I have on hand. The hole in the barrel was much smaller than 7/64” and my next size was much smaller. The hole on the gas block was 7/64”, the drill bit fit perfectly. I went ahead and opened up the hole on the barrel up to match the AGB since it can be shut down, being a little larger didn’t matter.

Second issue was the hole in the barrel and the hole in the AGB were not the same distance from the shoulder stop on the barrel. JP’s directions (had to look up and read on their web site) say to leave a .025 gap between the shoulder of the barrel stop and the gas block on military spec barrels. Well guess that measurement is wrong and the AR-Stoner needed a .052 gap between the AGB and the shoulder to make the center of the hole on the barrel match the center of the gas block hole.

So blowing air isn’t a sufficient process to make sure the holes line up.

Got it to work correctly, it cycles, feed second round and bolt hold open with my Fail Zero full auto BCG. Re-installed the JP Low Mass Bolt Carrier and it cycled correctly with hold bolt hold back on last round. Then I re-installed the Silent Capture Buffer Spring, still functioned correctly. Then I used the last few rounds of Wolf Ammo, it didn’t cycle. Glad I wasted it all on trouble shooting. Back to the Hornady VMAX and it still works correctly.

As a note, Wolf Ammo is less expensive, $17.99 per 20 but it is as dirty as my 22LR ammo. I will never save a few dollars and don’t recommend the ammo.

Moral to the story, measure EVERYTHING before assembly. This would have saved me $100 in wasted ammo. Now I can sight in my scope tomorrow. Fathers Day is going on today, Dad’s up from Florida.

[ricsmall]

we're all learning everyday tedward. Im glad you got it all worked out, and yes, the amax ammo will spoil you