6 ARC Gas Block Issue -- Need Help

[JimSC]

I am having a heck of a time getting a new 6 ARC build's gas block to seal well enough for the bolt to lock back on last the round. If it were a Grendel or a .223 I would just dump 50 or so steel case ammo through it and that has always helped. I have went through everything on this rifle including trying two lowers, various magazines, swapping BCG's, polishing the BCG, lighter buffers etc etc. In desperation I did try some blue LocTite on the gas block and gas tube and that did the trick for about 20 rounds then it blew out and the problem returned. Luckily I have a good selection of powders and 6 mm bullets from 68 gn through 107's. Suitable powders available either on my shelf, or on a buddies shelf would include. I am not concerned with accuracy or speed , I just want something that will produce enough carbon to seal that gas leak

TAC
Acc 2520
Leverevolution
LT30
LT32
AR Comp
Power Pro Varmint
H322
8208 XBR
Varget
IMR 4166

In your experience which powder would be the dirtiest burning

 

[6.5 forever]

I have used TAC. Definitely the dirtiest powder I have used.

 

[joshb]

I don’t think that’s the best way to fix the problem. I’d measure your block and barrel to check for fit.

 

[Gargoyle]

You must open your gas port .002"

 

[expiper]

you should try an adjustable gas block--or as stated change the port size--Roger

 

[jelenko]

^^ 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.

 

[dellet]

If the gas block to barrel fit is so bad you need locktite to seal it, and it still blows out, It's time for a new gas block.

A pinch or clamp type will fit tighter than a set screw type.

Enlarging the gas port will increase available gas to the system, but will also make the leak worse.

Using a slower/dirtier powder probably will work about as good as the locktite. High carbon build up is generally due to low pressure. once you switch back to the cleaner powder and likely higher pressure at the port, it will just blow the carbon out.

Lots of workarounds, just as easy to fix the real problem, if it is leaking that bad at the block.

 

[SG4247]

CFE 223 will make the most pressure at the gas port, and is also dirty as hell,

So, if it don't work, no other powder will.

I've burned prolly 30 lbs of it in the 6mmAR.

 

[JimSC]

I have used TAC. Definitely the dirtiest powder I have used.

thanks for answering my question.

As I said in original post, I have ran across this same situation in two previous builds. One of which was a custom built 6.5 Grendel upper, the other a home built .223. In both instances shooting 40 rounds of Wolf sealed the gas block. Unfortunately no PPU or Wolf 6 ARC exists

 

[A Marsh]

If its extra carbon you want just add graphite. Its already in powder anyway.

 

[JimSC]

If its extra carbon you want just add graphite. Its already in powder anyway.

great idea, thanks. I never thought of that. I spent a lot of Googling on this today and while results were all over the place on the dirtiest powder one thing that everyone seemed to agree with was that lower pressure loads were "sootier" than the high end loads. If this does not work next step will be ordering a non adjustable block. This thing is driving me nuts

 

[Walt Krafft]

Take the gas block off. Completely clean and degrease it and the barrel. Use Locktite stud and bearing mount when you put it back together. Put a tight patch in the bore at the gas hole to keep locktite out of the bore. Let it cure for a couple of days before firing. Stop trying to plug it with carbon. While you have it apart, see what is causing the leak. A lot of gas blocks have set screws to pull the block down. Add some if you can.

 

[Ray123]

I have 2 6mm ARC ARs never a problem.... with gas block or any powder I tried locking the bolt back...ya just don't go to dirty powder to fix your problem! I use adjustable gas block on 6 mm ARC and all "standard mil spec crap" that goes in all my ARs except 9mm...so the upper will run on any lower I own and not caliber specific.
There are other options besides "dirty powder" that actually work, with any reasonable powder....first is the gas block adjustsble? Does the barrel and gas block have a good fit?...measure the barrel gas block turned area to see if the Dia is undersized...and measure the gas block to see if its dia is oversize.
Then are the hole in the barrel and the hole on the gas block lined up? Measure the distsnces. Some adjustable gas blocks come closed off or partially so, with a requirement of .025 away from the gas block shoulder on the barrel...read instructions for your particular gas block.
And of all is correct & in alignment...check the size of the gas block hole, and enlarge it to the next numbered drill size or fractional size in the twist drill line up...no dirty powder required or needed.
Black powder comes to mind...lol.

 

[Gargoyle]

Open gas port - Harbor Freight numbered drill bit set. Use the round end as pin gauge. Find the bit that fits existing hole, then select the next larger bit.

Re-install gas block.

If still under gassed, open it with the next larger bit.

If over gassed, then add an adjustable gas block.

Strive for 3:00-3:30 brass ejection.

 

[JimSC]

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

 

[Gargoyle]

My Aero gas blocks are full open at 18 clicks...

 

[SG4247]

Again CFE 223 - reason I know is my Rifle was rifle + 3” and would run with CFE - WHEN NOTHING else would. I drilled gas port to .125” also.


Yours is +1”…

 

[JimSC]

CFE 223 will make the most pressure at the gas port, and is also dirty as hell,

So, if it don't work, no other powder will.

I've burned prolly 30 lbs of it in the 6mmAR.

unfortunately I have no CFE 223, but thanks for the suggestion. If the graphite trick doesn't work I may see if I can borrow a bit or buy a pound locally

 

[JimSC]

My Aero gas blocks are full open at 18 clicks...

this one is only 12 clicks from open to shut

 

[SG4247]

CFE223 is also the most accurate powder I’ve ever used in 6mm AR.