Gas Block Problem?

[Black Tail Hunter]

It sounds like from a previous comment that the mag may be the issue, if not are you using plenty of lube on the bolt carrier and buffer spring? Sometimes on new builds before the phosphor coating wears in on the upper and BCG you get more friction and inefficient cycling.

 

[ARlife4me]

I had a Wylde build not work correctly as built some time ago. Research then put me onto Spinco Spings. Used their selecting method and the recoil spring that they recommended got the rifle performing as it should. I've been using their recoil springs by default ever since.

Built a .308 from extra parts and ordered a Superlative GB for it (one of the very few parts I had to buy). I've been as impressed with it as I have been with the Spinco springs so those too are now a default choice for any non-std build. With a Spinco spring and the Superlative GB I did as the op did, started with the GB turned all of the way down and slowly opened it up until the bolt would lock back. One small step further and I set the locking screw.

I've become a fan of their springs also, but wish there was more selection on AR10 springs. I've been buying Odin adjustable buffers that helps tune.

 

[lyle2231]

I think he tried it wide open?

You're right! I didn't read all the posts before replying. Thinking out loud here, I wonder if the gas block/port is misaligned? How do you align your block? I use the breakaway plastic gage. So far this has been a reliable method. (Wanted to compare notes) Thanks!

 

[ARlife4me]

You're right! I didn't read all the posts before replying. Thinking out loud here, I wonder if the gas block/port is misaligned? How do you align your block? I use the breakaway plastic gage. So far this has been a reliable method. (Wanted to compare notes) Thanks!

I never knew the breakaway existed before? I use a bore scope.

 

[DDWing]

I know most of you are bolt gun guys, but maybe a few of you may have some suggestions for a fix. I have a AR10 in 6.5 CM that will not lock the bolt open on last shot. Wilson Combat adjustable gas block is full open.

Aero Precision M5 Upper & Lower
Wilson Combat Match Grade Tactical Hunter 18" SS Fluted Barrel
Wilson Combat nickel/boron BCG
Wilson Combat adjustable gas block & rifle length tube
VG6 Precision Gamma muzzle brake
3.8 oz. buffer, carbine spring

Ammo: Norma Whitetail 140gr. SP 2756 fps.

It could also be that the hole in your gas tube is not properly aligned with the hole in your gas block. I ran into that problem once on a 6.5 Grendel build.

I know most of you are bolt gun guys, but maybe a few of you may have some suggestions for a fix. I have a AR10 in 6.5 CM that will not lock the bolt open on last shot. Wilson Combat adjustable gas block is full open.

Aero Precision M5 Upper & Lower
Wilson Combat Match Grade Tactical Hunter 18" SS Fluted Barrel
Wilson Combat nickel/boron BCG
Wilson Combat adjustable gas block & rifle length tube
VG6 Precision Gamma muzzle brake
3.8 oz. buffer, carbine spring

Ammo: Norma Whitetail 140gr. SP 2756 fps.

 

[Kansaswoodguy]

If you have the correct gas tube then check gas block alignment with gas port hole in barrel and take a drill bit by hand no drill and run it into the gas port hole in the barrel. The manufacturers are very careful to not drill to deeply when making these holes so as not to harm the rifling and sometimes there is a small metal bur left behind that partially plugs the port.

 

[xsn10s]

If you have the correct gas tube then check gas block alignment with gas port hole in barrel and take a drill bit by hand no drill and run it into the gas port hole in the barrel. The manufacturers are very careful to not drill to deeply when making these holes so as not to harm the rifling and sometimes there is a small metal bur left behind that partially plugs the port.

Yeah that's what I read. I had a 308 AR10 so it was reliable from the get go. A common fix like said earlier was to oil the bolt assemble heavy as in dripping wet. And run some ammo through it to burn off the possible burr in the gas port. That would probably work the moving parts to fit together better also. That's the cheap easy thing to do. I also wondered if loading with a common 308 win powder like H4895 would help. Just a thought.

 

[bamban]

I started with the gas block at its lowest setting, putting one round in the mag. When the bolt did not lock open, I opened the gas block another increment. Kept doing this until it was fully open and still no bolt locking back.

Put a round in. With your non firing hand, press the bolt stop, keep it pressed when you fire the shot. If it is indeed the gas system is sufficient, the bolt will lock up.

If it locks back, look elsewhere for the problem.

Sometimes we have to trim the bolt stop spring a coil or two on the AR15 system. The mag spring has to overpower the bolt stop spring.

Let us know what the fix is.

 

[bamban]

On the few 20 inch AR308 type barrels I spun up with 0.750 gas blocks I used a smaller holes that AR15 types. 2mm as opposed to 0.096. No issues. I have no idea what production people put on their AR308 types.

 

[Lapua904]

Have you tried a different buffer? Get yourself another 3.8 oz buffer and try it. That's the first thing I would do.

 

[jasonco]

That buffer is a lot on the too light side, for a 6.5Creedmoor AR! An adjustable gas block helps, but you need a heavier buffer. In mine, I'm running 3 tungsten weights, just to get it running properly. My 6.5 Creedmoor AR10, has an occasional primer piercing issue, from it being a high pressure cartridge and Palmeto State Armory, not replacing the original gen 1 bcg, with their new, high pressure bcg assembly...still torqued off about that, but the rifle is a legitimate half inch rifle out to a 1000!

 

[bamban]

My 6.5 Creedmoor AR10, has an occasional primer piercing issue, from it being a high pressure cartridge and Palmeto State Armory, not replacing the original gen 1 bcg, with their new, high pressure bcg assembly...still torqued off about that, but the rifle is a legitimate half inch rifle out to a 1000!

I chambered a few 6.5CM from 18 to 26 inch barrels, we never shot half inch at 1000....just having fun... you probably meant half minute, right??

Cheers

 

[cohunt]

Buffer weight/spring rate/ and gas Blick hole size are all a balanced system. If the gas hole is larger than needed-- then you'll need a heavier buffer/spring

I have a 308 that uses an all plastic lightweight buffer (1 oz) and a titanium carrier-- hence the need for an adjustable gas block to limit the flow of gas back to the lighter weight components

It all has to be part of a balanced system to properly work.
Sometimes you'll need a bit stronger buffer spring to strip cartridges from a mag with a stiff mag spring too. It all comes into play.

 

[cactus02]

Check alignment of gas port and block. Check if bolt carrier is going all the way to the rear. If it is aligned and not going to rear check gas rings, they should hold the carrier up if the extended bolt is placed extracter face down on a table. If the bolt carrier is held up the rings are OK. The next to last thing is clean out the gas port on both the barrel and gas block. The last resort is to find the next size drill bit and open the gas port up a thousandth or two in the barrel. Use common sense and caution.