Large Frame AR Issues

[jda2631]

I just finished a large frame AR build. SLR receiver set, 308 proof barrel, SLR adjustable gas block, Rubber City Titanium BCG and bolt, and JP H2 SCS.

Went to shoot it Sunday for the first time, I shoot suppressed 95% of the time and only shot suppressed today. Cleaned the barrel a little and then lubed the bcg and started shooting. Started with gas block completely shut, shooting just some 147gr ball ammo. Was shooting 1 round at a time and opening gas block until bcg locked back on empty. Problem is even with GB fully open the bcg was still completely closed. With doing this on other guns, sometimes before I get to where it will completely lock back the bcg will be close to locked back but "stuck" resting on the mag about halfway back, I never made it to that. Bolt was still completely in battery each time. Switched to some factory 150 sst's and the same thing.

When I went to manually eject the spent shell, I had to mortar it on the table each time, was very difficult to get bcg to come out of battery after firing and eject the case.

Any info on where I should start looking to fix this would be greatly appreciated!

 

[padom]

I just finished a large frame AR build. SLR receiver set, 308 proof barrel, SLR adjustable gas block, Rubber City Titanium BCG and bolt, and JP H2 SCS.

Went to shoot it Sunday for the first time, I shoot suppressed 95% of the time and only shot suppressed today. Cleaned the barrel a little and then lubed the bcg and started shooting. Started with gas block completely shut, shooting just some 147gr ball ammo. Was shooting 1 round at a time and opening gas block until bcg locked back on empty. Problem is even with GB fully open the bcg was still completely closed. With doing this on other guns, sometimes before I get to where it will completely lock back the bcg will be close to locked back but "stuck" resting on the mag about halfway back, I never made it to that. Bolt was still completely in battery each time. Switched to some factory 150 sst's and the same thing.

When I went to manually eject the spent shell, I had to mortar it on the table each time, was very difficult to get bcg to come out of battery after firing and eject the case.

Any info on where I should start looking to fix this would be greatly appreciated!

Can you chamber and eject ammo manually without firing?? Was the bolt headspaced to the barrel? Did you try some match grade non-mil ammo like FGMM or Hornady?

 

[jda2631]

Can you chamber and eject ammo manually without firing?? Was the bolt headspaced to the barrel? Did you try some match grade non-mil ammo like FGMM or Hornady?

Yes, chambering and ejecting live ammo is no issue. It is a little stiff to get the bcg out of battery even with no round in the chamber, I just attributed this to stiff buffer spring with it being new. But this could be a different issue.

The barrel was not headspaced to the bolt, but I checked headspace with go no go gauges and it was good.

I used some Hornady Superformance 150 SST's, along with the mil ball.

 

[padom]

What do you mean its a little stiff? Does the Bolt go in and out of the barrel extension smoothly? So this issue happens when you fire ammo only and it does it with both ball and the 150 SST's.

If thats the case, sounds like a chamber issue. Did you have this spun up by a smith or buy it ready to go?

 

[jda2631]

I bought it ready to go, I assume proof does their own chambering with their AR prefits?

It is just harder to charge the rifle than other large frame AR's that I have. Takes more force to disengage the bolt and start the bcg traveling rearward, with no round or live round in the chamber. With spent round in chamber I have to mortar the rifle to get it to disengage and eject.

 

[padom]

Remove the buffer and then push bcg in front rear of upper then pull charging handle? Still hanging up/sticking??

 

[jda2631]

Ok, I will try that at lunch today.

 

[Greg Langelius *]

Connect some latex/silicone tubing to the gas tube where it enters the receiver. Blow some air through. If it does not pass air, check the gas block mounting for alignment with the barrel's gas port.

Greg

 

[hlee]

I had a similar issue with a JP barrel and bolt (and slr gas block) in 6.5 Grendel. Working the gas block from closed to open left the rifle not opening- had to mortar the rifle to get it open. I opened the block up full and had enough gas to run the rifle. Like yours, it seemed like it took more effort to manually cycle the action than in other rifles. I ran it full open for several mags to let the bolt and barrel extension surfaces wear in. Then, I worked backwards from convention for setting the gas block. I started at full open and went down until it would not lock back, then up till it did, then 2 more. Whatever was causing the hang up resolved over that range trip.

 

[jda2631]

I removed the buffer and spring, cycled the rifle. BCG moved freely, but was getting "stuck" in the buffer tube, gravity wasn't enough to have it come back out of the buffer tube. had to reach through ejection port and manually pull the BCG forward it wasn't difficult it just wouldn't come out without me putting some pressure on it. I've never actually done this with a rifle so not sure if that is normal. With buffer and spring back in it, it is running much smoother today than when I shot. I cleaned and lubed the crap out of it after I got done shooting.

I am going to double check gas block alignment tonight when I get back home. Maybe try some 175gr match ammo? See if the heavier bullets can cause enough pressure to cycle it?

Good to know @hlee

 

[padom]

Connect some latex/silicone tubing to the gas tube where it enters the receiver. Blow some air through. If it does not pass air, check the gas block mounting for alignment with the barrel's gas port.

Greg

This would not cause the bcg to hard seize preventing him from pulling the charging handle back.

 

[BLDTYLRY]

You've got a lot going on with your build: Adjustable Gas Block, Adjustable Gas Key on the BCG (i have the same BCG), and Silencer.

To start, I would setup/fire the rifle without the suppressor first to make sure everything is working. Either run the AGB fully opened and adjust the Gas Key or fully open the gas key and adjust the AGB. In my build I had no choice but use an Adjustable Gas Key as the Dracos barrel doesn't and cannot have a AGB.

 

[Greg Langelius *]

This would not cause the bcg to hard seize preventing him from pulling the charging handle back.

Absolutely correct.

It would also not prevent some other problem from causing the binding BCG.

I'd simply suggest that having more then one issue occur with a new build where using interacting parts from widely different sources are being combined for the first time. This is why I've decided, after doing the builds as a learning experience, to stick with factory designed, assembled, and warranteed rifles.

All that being said, all I'm trying to offer is the consequences of my limited experience where gas blocks and barrel ports did not align as expected. If I had to weigh my limited experience against yours, I'd most wisely come down very heavily in your favor.

That would still not affect the potentials in this question, or make my suggestion dead wrong without any further consideration.

We all get to have opinions on here.

Greg

 

[bigpeddler]

I had issues with the SLR as well... I ended up with a Superlative Arms adjustable gas block and it's great. For some reason I couldn't get the SLR to either stay consistent. I shoot match grade 168 Sierra ammo, so I think my ammo is not the issue. I also shoot suppressed.

Is your gas tube rubbing on your charging handle, causing extra friction? Did you space your gas block slightly off the shoulder of the barrel?

 

[aslrookie]

I had the same issue with an AR10 I built before. There are a couple things you can check:

Proof barrels use a really tight chamber (at least they did when I had one of their barrels in .260rem AR10) so factory ammo did not run very well. I had to reload ammo and bump the shoulder a little bit to get better fitment.

1) Separate the upper from the lower, remove the BCG, and put a round inside the chamber with your hand. It should just drop right in. Then point the muzzle upwards and see if the round falls out on it's own or if you have to tap it on the table for it to fall out. If it takes an excessive amount of force to remove the round from the chamber, you should be contacting proof research. Just an FYI, they will probably tell you to try prime ammo before issuing you an RMA to send it back for inspection.

If number 1 passes that check:

2) Inspect the BCG for burrs. I had a JP bolt carrier that a burr inside of it which was causing the added friction of extracting a round manually. JP replaced the carrier for me. The bolt should move freely inside the BCG, so if it's taking more effort than usual to move the bolt in/out that would be my next thing to look at.

I fought with my build for weeks trying to figure it out. Sounds like you're having a similar issue as I did.

 

[jda2631]

I had issues with the SLR as well... I ended up with a Superlative Arms adjustable gas block and it's great. For some reason I couldn't get the SLR to either stay consistent. I shoot match grade 168 Sierra ammo, so I think my ammo is not the issue. I also shoot suppressed.

Is your gas tube rubbing on your charging handle, causing extra friction? Did you space your gas block slightly off the shoulder of the barrel?

Do you mean is the gas key rubbing inside the charging handle? I don't believe it is. I don't feel anything like that cycling it and there is no wear inside the CH.
Gas block is against the shoulder of the barrel, I measured the gas port in the barrel and in gas block and the port in the barrel should be well within the port of the GB.

I had the same issue with an AR10 I built before. There are a couple things you can check:

Proof barrels use a really tight chamber (at least they did when I had one of their barrels in .260rem AR10) so factory ammo did not run very well. I had to reload ammo and bump the shoulder a little bit to get better fitment.

1) Separate the upper from the lower, remove the BCG, and put a round inside the chamber with your hand. It should just drop right in. Then point the muzzle upwards and see if the round falls out on it's own or if you have to tap it on the table for it to fall out. If it takes an excessive amount of force to remove the round from the chamber, you should be contacting proof research. Just an FYI, they will probably tell you to try prime ammo before issuing you an RMA to send it back for inspection.

If number 1 passes that check:

2) Inspect the BCG for burrs. I had a JP bolt carrier that a burr inside of it which was causing the added friction of extracting a round manually. JP replaced the carrier for me. The bolt should move freely inside the BCG, so if it's taking more effort than usual to move the bolt in/out that would be my next thing to look at.

I fought with my build for weeks trying to figure it out. Sounds like you're having a similar issue as I did.

When I put a bullet in the barrel, if I turn the gun vertical the bullet doesn't fall out on its own, but a very light tap and it falls out. Takes very little effort.
I can't find any burrs on bolt or bcg, on the inside or outside of bcg.


Like an idiot I took my gas block apart at the range to inspect it and dropped and lost the plunger/detent for it. Slr is sending a new one, but testing is on hold till its gets in...