6 ARC Gas Block Issue -- Need Help

[nakneker]

Like I said earlier all I really wanted was an opinion on a dirty powder. But here is the info on the gun and the problem
here is the build -

22" barrel by Precision Firearms, Aero upper, Aero BCG and bolt, Aero handguard, Aero adjustable gas block, Odin Works carbine adjustable buffer , Rifle + 1 gas tube

First lower is a older Rock River Match, the second is a newer Palmetto Armory. Both lowers work fine on a pair of Grendels and a .223

what I have tried so far

As far as the gas block goes I have uninstalled and reinstalled at least 5 times, when I reinstall I use a borescope looking up through the gas port in the barrel to make sure it is perfectly aligned. From that perspective it looks like the barrel gas port is larger than the gas block port. The two setscrews are torqued to 30 inch pounds IAW manufacturer instructions. I have went from 1.9 oz on the buffer to 4.2 or whatever the three tungsten's are. At the moment it is 1.9. Gas block is fully open @12 clicks

Upper has been mounted on 2 lowers, and I have tried both a BobSled and 2 brands of magazines all of which of which work perfectly with other uppers. I have also tried 2 other BCG's and bolts again all BCG's work perfectly in my two Grendels. It feeds perfectly from different magazines and with just the aluminum weights in the buffer and gas block wide open it is acting as if it is over gassed with the ejected cases landing between 3 o'clock and 2 o'clock instead slightly behind at 4 - 5 oclock.

The only time it has locked back was the first 20 rounds after I wicked some blue LocTite in around the gas block and let it cure for a day. That was with both magazines and Bobsled. Yesterday when I went back to the range it once again started the same old behavior refusing to lock back after the last round. I am 99% sure the heat from the gas melted the loctite and pushed it out, which I assumed would happen. That gas is a lot hotter than any flavor of loctite. The only reason I tried it to was to nail down the problem to gas block leakage which it did.

The carbon trick has worked for me twice before, once on a home grown .223 the other a custom built 6.5 Grendel upper by a well known builder. He was the one that first turned me onto that trick. It works, I have seen it cure the problem twice. I am going to try the graphite trick A Marsh suggested and if that does not cure it in 30 or so rounds I will be ordering another gas block, it that does not cure it I will be sending the barrel back and see if the maker can figure it out

Frustrating Jim. Hopefully a solution comes and you can enjoy the gun sooner rather than later. That kind of stuff will drive a guy nuts.

 

[JimSC]

But...
you should be able to correct the over gassing by dialing the adjustable block closed.

yep, early on . Might try again when I take the gun back to the range. Got some new bullets and powder for for the grendel so I am taking it tomorrow for a load workup

 

[Twdmar]

Over gassed guns will lock back on last round for sure. I look for:

Brass ejecting prior to 2:30
Ejector smears on case head
Brass just barely hopping out of the ejection port or stove pipes. (Means bolt operating too fast)

If I drill the gas port too big the only savior so far is a bleed off adjustable gas block, like Superlative Arms. Restrictive gas blocks don't help, even the restriction setting on the Superlative Arms doesn't help.

The part about over gassed rifles locking back all the time is probably correct most of the time. I would add that I've seen the dpms pattern ar10 barrels that were way overgassed would occasionally not lock back. My guess is that if there is too much gas and the gas system is too short, the brass case, once it has expanded and grips case wall, does not have quite enough time to let go before the bolt moves back.
The fix for that, including things like the o-ring under the extractor etc, along with the case not letting go, slows the bolt enough to limit locking back.
That doesn't really make the problem of being over gassed more apparent but I would add it could be a symptom too, to not discount it as undergassed.

 

[Twdmar]

yep, early on . Might try again when I take the gun back to the range. Got some new bullets and powder for for the grendel so I am taking it tomorrow for a load workup

Can you take something like one of those silver sharpies and see how much is rubbed off of the gas block and check fit? Possibly one factor you can eliminate

 

[Ray123]

reread my post, I don't have a Aero barrel.

On another note. I looked at my gas block and the barrel in front of it last eve and see no signs of any gas leakage at all. What keeps bugging me is the ejection pattern which indicates over gassing, not under gassing. Is it possible for the BCG to be traveling too fast ? Or maybe the bolt is binding a bit preventing it from catching on the empty magazine catch?

Oops, I miss read, on the Areo upper, thought is was a complete upper from them, as was my first ARC which the barrel was inaccurate.

What is the gas port size in your barrel?
I thought it worked when loctite was applied to the gas block for a few rds.
But it's over gassed? Heavy over gassed would tend to rip the rims off cases.
Your loctite experiment, seems to suggest you don't have enough gas and/ or it's leaking.
Is the adjustable gas port working properly?
Turn it all the way down, and open it a few clicks at a time... is there a difference? Try a different gas block.
Install another new bolt catch and spring...or one from a working rifle that locks the bolt back..as it appears that is a problem.
Try the upper on a different lower... incase something is slightly out of spec in the bolt catch lower area.
Does your ammo have enough gas to run the system?...try a box of quality factory ammo.
Can you blow a full volume of compressed air through the gas tube ...gas tube correct length?
Inspect the bolt, type 2? Carrier, gas rings, gas key staking, wear pattern on bolt barrel extension or in reciever.
You can use LocTite green high temp bearing sleeve type loctite for more strength and temperature up to 650°...as a last resort IMO.
Without inspecting the components, and measuring them, like the gas port dia...etc, of this build its hard to guess at all the possibilities that could be causing the problem.
Maybe trying some of these suggestions posted will help...also if you have a AR knowledgeable friend help you go over these items and look for problems..might be of help.
Remember...Frustration is a waste of energy and clouds the mind.
Stay determined and focused. Good luck.

 

[JimSC]

What is the gas port size in your barrel?

no idea

I thought it worked when loctite was applied to the gas block for a few rds.

for about 20 rounds it worked perfectly, both with magazines and the Bobsled, thought I had the problem licked or at least narrowed down

But it's over gassed? Heavy over gassed would tend to rip the rims off cases.
Your loctite experiment, seems to suggest you don't have enough gas and/ or it's leaking.

yep, that is what is driving me nuts, just going by case ejection it looks over gassed. Cases land way out there between 3 and 1 o'clock

Is the adjustable gas port working properly?
Turn it all the way down, and open it a few clicks at a time... is there a difference? Try a different gas block.
Install another new bolt catch and spring...or one from a working rifle that locks the bolt back..as it appears that is a problem.

tried 2 lowers, both work fine on three other uppers. Tried on 2 other Grendel BCG's. All three BCG's work fine on the Grendels

Does your ammo have enough gas to run the system?...try a box of quality factory ammo.

reloads have went slightly past gas gun recommendations, once again the case ejection shows plenty of oomph

...also if you have a AR knowledgeable friend help you go over these items and look for problems..might be of help.
Remember...Frustration is a waste of energy and clouds the mind.
Stay determined and focused. Good luck.

had an AR guru at the club give it a quick once over after a ARA match a couple of weeks back , he was as puzzled as I am.

I will get it back to the range to play with the gas block adjustments. If it continues to malfunction I will be replacing the gas tube and block. I am going to the range tomorrow and try a few rounds starting with the gas adjustment at 25%, If that does not work it's time to get a new block and tube

edited for clarity

 

[JimSC]

mixed messages from todays session. I was just using up odds and ends of ammo. I started with gas block
open 25% and 2.4 oz buffer. Kept opening gas block 2 clicks at a time until it began ejecting and toward full open and it actually started locking back. That was with 100gn Hornady interlocks and 29.0 gns of 2520. According to GRT that would have been 5 K over gas gun pressure but according to my chrono data I was 15k below that. No brass indicators of OP but then that would not show up until I was far into blot gun territory. Ejected cases made a nice pile at was at 3 o'clock about 5 feet out

No other ammo gave me lock back. I am going to load some more ammo on the border of bolt gun pressures/velocities hoping I do not sheer a lug, maybe order one of the heavier duty BCG's to keep in the range bag.

 

[Twdmar]

mixed messages from todays session. I was just using up odds and ends of ammo. I started with gas block
open 25% and 2.4 oz buffer. Kept opening gas block 2 clicks at a time until it began ejecting and toward full open and it actually started locking back. That was with 100gn Hornady interlocks and 29.0 gns of 2520. According to GRT that would have been 5 K over gas gun pressure but according to my chrono data I was 15k below that. No brass indicators of OP but then that would not show up until I was far into blot gun territory. Ejected cases made a nice pile at was at 3 o'clock about 5 feet out

No other ammo gave me lock back. I am going to load some more ammo on the border of bolt gun pressures/velocities hoping I do not sheer a lug, maybe order one of the heavier duty BCG's to keep in the range bag.

That would be super frustrating and quite expensive just in driving expenses.
I re-read everything posted. The first thing I would do I eliminate errors outside of the operation like assembly/production errors. Think things like the wrong ejector spring, ejector out of spec etc. There are also 2 different grendel bolts. Eliminate all the variables. Parts are made on Monday mornings and Friday afternoons all the time.
Check the barrel extension out too.
Where brass lands is a good indicator for operation on a 223, it may not be with other cartridges so I would not consider it an absolute here. Or really anywhere, again because of things being out of spec etc.
If you have used multiple, known to be functional lowers and held down the bolt stop, consider that to not be your problem. You've tried different buffers.
Like Walt said, check gas key, gas tube, gas rings etc. If those are good, then it's either gas port, gas block fit and gas system length. Those are not things I think you're likely to fix with a dirty powder.
I think you're wasting your time and money for now. Try to get a gas block that fits tight and check the barrel diameter. It sounds like not enough gas if the loctite worked. So I would think loose gas block or undersized port.
Good luck!

 

[JimSC]

That would be super frustrating and quite expensive just in driving expenses.

Luckily I am retired and only 15 min from the range. I made a career out of solving problems, and developed a good rep as a trouble shooter. It wasn't that I was all that smart but I just never knew when to give up. Getting several solid lock backs on the ARC plus the fact that my newest Grendel is grouping well at 100 and is ready for some mid and long range playtime made for a good day.

 

[Gargoyle]

Luckily I am retired and only 15 min from the range. I made a career out of solving problems, and developed a good rep as a trouble shooter. It wasn't that I was all that smart but I just never knew when to give up. Getting several solid lock backs on the ARC plus the fact that my newest Grendel is grouping well at 100 and is ready for some mid and long range playtime made for a good day.

I got to fix an over gassed AR10 today. Thank heavens I got my bull 20" 308 corrected with a Superlative Arms bleed off gas block! Before it was blooping brass just 6 inches from the gun. Heavily overgassed. The SA gas block has 48 bleed off settings with 17 setting acting like a regular gas block. Started at 30 out and ended at 36 out. 80rnds through it with load development of 168gr + 155gr Amax, and some Hammer Bullets 137gr Hunters.

 

[Bamban]

^^ This. [In response to joshb's post]
Also, some AR barrels have their gas port in a slightly different position such that there needs to be a small gap between the gas block and the 'shoulder' of the barrel at the breech end of the gas block tenon.

Opening the gas port also came to mind, but not sure that's the issue if sealing the area with loctite worked.

You are right, I've seen gas blocks with ports varying from 0.275 to 0.310 from the edge. I run all my barrel gas ports at 0.300 from the shoulder, and cut an alignment pad 180 out from the port.

Clamp on blocks tend to clamp and seal better than screw ons for undersized journals.