Confusing 6ARC AR15 Gas Issue After Switching to Rifle +1 Barrel
- Thread starter TheyCallMe64
- Start date
Most local smiths probably don't know that much about ARs or scope barrels that often.
@TheyCallMe64 - You never confirmed! Did your gunsmith remove the old gas tube & replace it with the one that should've shipped with the Proof???? If he doesn't know much about AR's he may not have. Plus 1" is not that common & doesn't look much different than a rifle length tube.
Confirm that tube is correct first or you'll just be chasing your tail.
If it is indeed the correct tube then drill the port .003-.004 as has been suggested. I'd lean towards .004 since you want to run fast powders. Sharp bit and go slow. I try my best to get mine about in the middle of the gas block adjustment. Drilled my rainier ARC barrel .002 & my Craddock .003. I'm also running light weight carriers with std wt silent capture springs. Both of those are pretty close to middle of the gas block running Lever.
Brownells & Proof gave you bad advice. Every time there has been a function issue with a Proof, Rainier, or Craddock 6ARC on here it's been to small a port and under gassed. If your under gassed, you need to either drill the port (increase gas volume) or lighten up the reciprocating assembly (reduce gas requirement) period.
They don't seem to understand dwell time or are misapplying an aspect of it to their reasoning. The best way to think of dwell time in an AR = the distance between the gas port and crown. In other words how much time does the pressure have to do the required work to the carrier. Likewise how much engagement does the gas tube have in the carrier key (why the tube length is so important).
Telling you to add weight or a heavier spring is a bad attempt to increase locktime. This is a band aid fix usually applied to gas systems that are to short like carbine length on a 16" or 18" barrel. They unlock to early, are hard on parts, & very intolerant of hot loads.
Confirm that tube is correct first or you'll just be chasing your tail.
If it is indeed the correct tube then drill the port .003-.004 as has been suggested. I'd lean towards .004 since you want to run fast powders. Sharp bit and go slow. I try my best to get mine about in the middle of the gas block adjustment. Drilled my rainier ARC barrel .002 & my Craddock .003. I'm also running light weight carriers with std wt silent capture springs. Both of those are pretty close to middle of the gas block running Lever.
Brownells & Proof gave you bad advice. Every time there has been a function issue with a Proof, Rainier, or Craddock 6ARC on here it's been to small a port and under gassed. If your under gassed, you need to either drill the port (increase gas volume) or lighten up the reciprocating assembly (reduce gas requirement) period.
They don't seem to understand dwell time or are misapplying an aspect of it to their reasoning. The best way to think of dwell time in an AR = the distance between the gas port and crown. In other words how much time does the pressure have to do the required work to the carrier. Likewise how much engagement does the gas tube have in the carrier key (why the tube length is so important).
Telling you to add weight or a heavier spring is a bad attempt to increase locktime. This is a band aid fix usually applied to gas systems that are to short like carbine length on a 16" or 18" barrel. They unlock to early, are hard on parts, & very intolerant of hot loads.
Thanks. That'll help me sleep better...
This might be the case. He didn't seem familiar with his little barrel scope and said it was new.
I'll give him one thing - he made sure the barrel and upper were a whole lot tighter together than the factory barrel and upper were. But that's a story for another time.
Hi @357Max - Yes, he definitely used the new Proof gas tube. At first, he told me he didn't need it and would reuse the old CMMG one. But when I told him that this one was a rifle +1 length, rather than the rifle length that the old barrel had been, he said, "Ope, yep, definitely need that then." So he knew, and gave me the old one back.
I'm like you - I'd really like to aim for middle of the gas block adjustment so I have some forgiveness in each direction.
I've never drilled one myself though and am a sales guy - definitely not a DIY kind of guy - so I'll probably take it to my gunsmith. He may not be the best around, but I don't think he's an idiot and he's certainly better than I am.
It sounds like a lot of people have had this issue as you stated. You'd think Proof would take notice, but then again, there's a negativity bias with posts you see on the web and the majority of their customers probably have no issues.
The good side to all this is that I'm getting a great education in ARs. Never questioned the parts on my 5.56 and 300 blk - just bought them and ran them.
I've acquired a set of pin gauges. My gas port measures .093 on the money. I will ask a local machinist to open it up to .098.
FINAL UPDATE (I hope!)
Problem solved!
Local machinist found a bit of a burr in my gas port possibly restricting gas flow. Although the hole "measured" 0.093", the burr prevented larger pin gauges from entering the hole all the way when held to one side. So effectively, it was more like a .075ish" hole.
He opened my port up to .100" and removed the burr in the process. This was a little more than .098" but I did not feel like having to do this twice in case the burr wasn't really the problem. Figured we'd oversize it, then choke it down with the adjustable gas block.
Gun appears to be running Varget loads fine. Gas hole was definitely the problem.
Thanks to everyone who weighed in with advice!
Problem solved!
Local machinist found a bit of a burr in my gas port possibly restricting gas flow. Although the hole "measured" 0.093", the burr prevented larger pin gauges from entering the hole all the way when held to one side. So effectively, it was more like a .075ish" hole.
He opened my port up to .100" and removed the burr in the process. This was a little more than .098" but I did not feel like having to do this twice in case the burr wasn't really the problem. Figured we'd oversize it, then choke it down with the adjustable gas block.
Gun appears to be running Varget loads fine. Gas hole was definitely the problem.
Thanks to everyone who weighed in with advice!
Proof didn’t deburr the GH, shocking. Good news that you found the likely culprit though.
Just for future reference the top notch AR specialists use a carbide reamer to finish up the gas port hole they don’t leave a burr inside like a drill will. Also once you’re done drilling add a little chamfer to the top of the hole on the barrel it helps if the gas block is ever so slightly off and prevents a burr up top. Awesome to hear it’s running good now.
This was insanely helpful. I feel like I’m taking crazy pills as I’m having the exact same problem with mine, and I’ve tried multiple buffer weights/springs. I’ll be sending this back to Proof to have them analyze.
Thank you, thank you, thank you for this detailed description @TheyCallMe64!
Wondering if the material wasn’t pushed down into the bore, causing damage on its first firing.
I once drilled out a gas port on a ballistic advantage barrel, which lead to the exact situation stated above. This didn’t affect the, already terrible accuracy of the BA, but left noticeable markings on the rifling as the bullet carried it down the bore.
I once drilled out a gas port on a ballistic advantage barrel, which lead to the exact situation stated above. This didn’t affect the, already terrible accuracy of the BA, but left noticeable markings on the rifling as the bullet carried it down the bore.
Honestly didn't think to check; I've been making impacts easily at 1000 ever since and am really happy with the whole setup now nearly a year later.
This post just totally saved me. I have the almost exact same set up issue with an 18 inch proof barrel rifle plus one and for the life of me couldn’t understand why the factory loads would cycle and my Varget loads would not. Tried infinite combinations the last 2 months, including a new BCG and bolt and way to heavy of a powder charge. I was getting really bad burrs in my alpha brass as well. Not good. I was just about to finally invest in some Leverevolution or maybe in N540 but if I can minimize my powder selection/storage and keep Varget since I use that for my 6 Dasher, it makes everything better(and hopefully more accurate). I will be going to my gunsmith to see if they can take a look at my gas port and open it up to 0.098 or 0.10. Thank you so much.
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