6MM ARC New Barrel set up. Teething pains not cycling

[Canuckienns]

Swapped out my 223 24 inch Criterion for a 22 in + 6 mm ARC. Using a JP Hp bolt. Adjustable gas block fully open.
Working on up with starting loads Varget and Sierra 107's. Accurate from the get go. Right up to 26 GR.
JP captured spring system weight 7.3 Oz Will not cycle
JP captured spring system lightest spring 6.3 Oz. Will not cycle
Standard rifle buffer weight and Tubbs flat wire. 5.3 Oz. will not cycle
Standard rifle buffer weight and std silicone spring. 5.3 Oz will not cycle.
Very accurate and will not cycle.
I will use lighter buffers tomorrow.
What say ye!

 

[DonB]

Are you sure your gas port on the barrel and gas block are aligned?

 

[troupe]

Did you say it was a + gas system ? Never been a fan of the + systems. If everything is lined up in the gas system, how light is the buffer system ? Make sure the lugs are releasing good on the extension and not dragging. Most likely not, but worth the check. Is the gas block used, could be carboned up.

 

[NZ_Fclass]

A while back I had a similar issue that was cured by moving the gas key ( is that correct) on the bolt, so that the gas tube went in deeper. A small amount of shift did the trick.

 

[Canuckienns]

Troupe thanks I will check. I have been building custom Ar15 and Ar10's by the score for years. First time on an ARC and plus +2 gas system. In my original post you can see counting down the buffer weights and springs. Next ones to come will be carbine H3 and silicone spring 3.3 ounces with a spacer in a rifle length tube.
Standard carbine buffer next is 1.8 OZ.
I normally get paid to trouble shoot, so I am being very systematic.
Oh yes adjustable gas tube is new Superlative arms.

 

[Daddycaddie67]

You’ve worked through the gas block settings and still won’t cycle correctly?

 

[Canuckienns]

Everything with the gas block is correct. I went down to the lightest buffer weight and springs. No cycling
So I am suspecting that the JP high pressure bolt is leaking by in the carrier. I bought new JP bolt and used a Fail Safe NB carrier that was used with a 556 set up recently and never missed a beat in competition. I swapped out the Fail Safe carrier for a PSA new one and there seems to be a much better seal arounds the rings. Load up some more and off to the range tomorrow.

 

[SecondsCount]

This guy had to enlarge his gas port

6mm ARC cycling issue

I tried to go back and read others who have similar builds and my problem is a little different (or maybe it's not). I have an Odin 18" rifle + 2" 6mm ARC barrel with a Superlative Arms adjustable gas block. Initial setup with with an H buffer. Loaded a Duramag 6.5 grendel mag with 1 round each...

www.snipershide.com

 

[chromatica]

I have a Ballistic Advantage 24 inch barrel and could not cycle with an H2 buffer (using Armaspec Stealth Recoil Spring). I called the vendor and the recommended H1 for 6 ARC. That worked for me.

 

[Canuckienns]

In my last last post I stated I used an H1 buffer weight. The next logical step after replacing the BCG will to be enlarging the gas port.

 

[Lone Hunter]

This guy was having trouble with the 6ARC to. You might find some help here.

Need some troubleshooting help: Bad Gas Block or Out of Spec Bolt Catch

Upper: VLTOR MUR-1A Barrel: Proof Rifle+1 Gas system, 6mm arc chamber, 18" barrel length, model 128688 Handguard: CMT HDM Arca 17" Gasblock: Superlative arms Clamp model .750 gas journal Gas tube: Proof supplied with barrel, rifle+1 length BCG: CMC Triggers 6 arc enhanced, bolt headspacing...

forum.accurateshooter.com

 

[msalm]

W/ the +2 gas, the gas port will need to be larger, what is the diameter now? Minimum would be .093” in a 5.56 (rifle length gas), the ARC with its larger bore and slightly larger case capacity would be similar I think. With the adjustable gas block I’d open it up to .100” (or a bit more) and just throttle it down to where it works correctly. There used to be a high power website (NJ high power?) that had some information on gas port sizes for various +2 gas systems in different barrel/caliber configurations…may have been mostly AR10 based but still good reference material.

 

[troupe]

Your bolt carrier and bolt should be able to stand on end with the bolt extended as if in the ejection form. The rings should be able to support the weight with out the bolt closing to the in battery position. Also make sure your rings are gapped correctly, which I am sure you already know this.

 

[Canuckienns]

Yesterday the fully open gas block and the swapped out BCG ejected every time with a H3 and a standard buffer weight, but did not back at any time. Troupe thanks, bolt and rings is good. I think that an enlarged gas port is in order.

 

[kilowatt41]

My son is having the same issue with his 6mm ARC. He’s 18” bbl with a carbine spring and buffer with a rifle +1system, adj gas block full open. Very light ejection and doesn’t lock open or pick up another round.
I believe he said it had .086 gas port.
This sounds pretty common when I started reading about it, I suspect that he will have to open the gas port a bit more.

 

[Canuckienns]

Porting by Black and Decker?

 

[Canuckienns]

I hit 19 out of 25 steel targets 8 inch yesterday in a competition. Single shot ejecting brass, no lock back, Bob's Sled. 627 yards.

 

[kilowatt41]

Factory Hornady black cycled in my son’s rig. I guess we’ll have to find another powder combo to try. Varget and H4895 would not generate enough energy to cycle .

 

[mic2377]

Try using a non adjustable gas block that seals better. I had a very lightly gassed AR barrel that I had initially used an adjustable gas block with that I did not realize was rather leaky, in that it had obvious fouling from leakage around the adjustment screw and gas tube. I had switched to a VLTOR clamp on style that sealed much better and cycling problems were solved.

That being said, it still may be necessary to enlarge the gas port should this fail.

 

[Canuckienns]

I picked up the 6 ARC AR 15 from my gunsmith who enlarged the gas port yesterday. It cycles like a champ with my Varget and Sierra 107 match kings loads. There was not gas leakage in the gas block, Now I can tune the rifle with various buffer weights and spring and gas to get it where I want it to be in long range competition.