Dirty vs Clean barrel COAL

[Coyote Kev]

This could go in the semi auto forum, but it applies here as well. I built a DPMS style AR10 and put a proof research carbon fiber barrel in 6mm creedmoor on it. When I got the barrel new I measured the COAL to the lands with several different bullets. They all measured longer than I would ever load them. I have been having failure to feed problems. It never happens when the barrel is perfectly clean but it doesn’t take much fouling before it starts. It also seems to happen sooner and worse the colder it is out. At single digit temps, it will fail after as few as 6 shots. When it was 25-35 degrees or more it would start to fail after 20-30 shots. When I say fail, the bolt picks up the next round but stops when the round is 7/8 in the chamber. The bolt and extractor don’t lock around it. So you have to drop the mag and pull the charging handle back and let it slam on the round. This seems to happen randomly meaning it could be the 3rd or 8th shot or every other shot.

So when studying what was going on I took some live rounds and pushed them with my finger into the chamber. There was definitely some resistance the last 0.1 to 0.2 inches. When I extracted those rounds they all had scuff marks on the bullet right about the ogive and back toward the case neck that were about 0.1 inches long. They were on the entire circumference of the bullet. So I measured the COAL again in the barrels dirty state. To my suprise it was much shorter than what I measured with the barrel new. I thought I messed up on my initial measurements but after a good cleaning, and measure again, the COAL was the same as when measured new. To be specific, my 87 VLD measures 2.21 inches with ogive at the lands when clean. It measured 2.073 after just 60 rounds. This doesn’t seem normal to me, but could explain my failure to feed issues. Any thoughts.

 

[spife7980]

Yep. Building up carbon deposits can do that. Not that severely usually... but it it goes back to where it was before when cleaned then you have your answer.

I would consider a different powder myself, where you using rl16 or h4350. I suspect one of them...

I’d ask myself if there is something I could do to limit the shortness coming back into the chamber and if you are really cleaning it all as thoroughly as you think you are.

 

[Coyote Kev]

Yep. Building up carbon deposits can do that. Not that severely usually... but it it goes back to where it was before when cleaned then you have your answer.

I would consider a different powder myself, where you using rl16 or h4350. I suspect one of them...

I’d ask myself if there is something I could do to limit the shortness coming back into the chamber and if you are really cleaning it all as thoroughly as you think you are.

I’m using Varget. In my limited experience it’s cleaner than h4350. This seems to happen after very few shots. I’ve never noticed this in my 260 Rem burning H4350, also an AR10. I should note that I shoot all my rifles 100% suppressed.

 

[clcustom1911]

My Proof chamber is A LOT tighter than my stock chamber based on the shoulder diameter of fired casings. On my stock RPR barrel, the shoulder would be +.004 wider after firing. With the Proof Barrel, the shoulder diameter is +.001-.002 after firing.

Yours may be tighter too.

 

[Coyote Kev]

My Proof chamber is A LOT tighter than my stock chamber based on the shoulder diameter of fired casings. On my stock RPR barrel, the shoulder would be +.004 wider after firing. With the Proof Barrel, the shoulder diameter is +.001-.002 after firing.

Yours may be tighter too.

I thought this was the problem and actually sent it to Proof to measure. They said it was “tits” and would not advise opening it up more. They said they had guys building AR10s in 6CM for competition and they thought my chamber dimensions were ideal. I feel like they put a bolt chamber on an AR barrel. Those dimensions just don’t work. Especially running suppressed.

 

[spife7980]

I completely blanked over the 87 vld... duh. Faster powder, not slower like I was thinking.

Do you have an adjustable gas block?

Are you using frog lube in ample quantities that could be solidifying at the colder levels and dragging the whole system down with it? I’m curious after a good clean and single digit temps if it does it ran dry for 10 shots or so.

For measuring your lengths, are you going to hard stop or first touching?

 

[Snuby642]

Would taking shoulder measurements on round fired in dirty chamber, then figure bump from that fix it?

 

[Coyote Kev]

I completely blanked over the 87 vld... duh. Faster powder, not slower like I was thinking.

Do you have an adjustable gas block?

Are you using frog lube in ample quantities that could be solidifying at the colder levels and dragging the whole system down with it? I’m curious after a good clean and single digit temps if it does it ran dry for 10 shots or so.

For measuring your lengths, are you going to hard stop or first touching?

So the lube could be part of the problem. I'm using Wilson combat oil. Supposedly "made from the slickest stuff known to man" I looked at the bottle and was surprised to see it's only rated down to 10 degrees F. I have since cleaned all that out and put some Birchwood Casey synthetic oil on it which is rated much lower. But I still don't get the huge change in COAL. To me first touching and hard stop are the same. I'm using the Hornady tool.

 

[Coyote Kev]

Would taking shoulder measurements on round fired in dirty chamber, then figure bump from that fix it?

Interesting idea. I'm already using a Small base die that bumps it back to New brass measurements.

 

[clcustom1911]

Does the rifle have the same issue while shooting factory ammo while suppressed?

Does the rifle have the same issue with the reloads unsuppressed?

 

[clcustom1911]

Reference lubrication: Militec-1 has a "pour point" down to -45 Fahrenheit. Meaning it stays liquid down to -45.

Militec-1 Technical Info

Ever since I found and used a small 1/2 Oz. Tube worth of it in Iraq back in 2005 on an Army base, it's all I will ever use on any of my firearms. A 16 Oz bottle will last you forever for firearms use. I also use Militec-1 grease for my lugs on my bolt guns, AR barrel nut, grease fittings on my truck...

You get the idea LoL. I LOVE MILITEC-1

 

[spife7980]

Interesting idea. I'm already using a Small base die that bumps it back to New brass measurements.

That could be contributing to letting a bunch of debris in the chamber? Try only bumping the shoulder back just enough to chamber and all the way back to minimum spec.

 

[Coyote Kev]

Does the rifle have the same issue while shooting factory ammo while suppressed?

Does the rifle have the same issue with the reloads unsuppressed?

Yep same problem with factory loads. And I refuse to shoot unsuppressed. Just plain uncivilized.

 

[clcustom1911]

....... And I refuse to shoot unsuppressed. Just plain uncivilized.

????

I wish I had the choice to be "civilized" !!! Stupid California

 

[Coyote Kev]

Another piece of info... I’m shooting Lapua brass with small rifle primers and using CCI 450s. Could this be poor powder ignition and thus extreme fouling?

 

[Snuby642]

In ar 15 we add some tungsten to slow the bolt opening on suppressed barrels.
Has kept my chamber cleaner I think.

 

[Coyote Kev]

In ar 15 we add some tungsten to slow the bolt opening on suppressed barrels.
Has kept my chamber cleaner I think.

I'm currently waiting on a Odin adjustable weight buffer and plan to run it heavy. I already have an adjustable gas block adjusted correctly. Also the proof barrel has a really long gas system (rifle +3). That decreases the pressure and should slow bolt opening.

 

[Snuby642]

Sounds like you have that well taken care of.

Running out of straws to grasp.

I had a similar problem in the cold due to hundreds of rounds of dirt and slugged lube from hot weather congealing but a quick cleaning with a bore snake got me going again.

Never seen one clog so fast.

Have you cleaned your can recently?

 

[Coyote Kev]

Just cleaned it with the rifle. Havnt shot it since. But boy was that thing dirty. Soaked in CLR overnight and still could barely get the baffles out.

 

[Coyote Kev]

Reference lubrication: Militec-1 has a "pour point" down to -45 Fahrenheit. Meaning it stays liquid down to -45.

Militec-1 Technical Info

Thanks. Sounds like some good stuff.

 

[Snuby642]

Dirty probably not much effect.
Full / restricted could put a lot of extra fouling in the chamber possibly.

 

[clcustom1911]

Thanks. Sounds like some good stuff.

It's the shizzle of the nizzle. Get it here!!

 

[Coyote Kev]

That could be contributing to letting a bunch of debris in the chamber? Try only bumping the shoulder back just enough to chamber and all the way back to minimum spec.

This would imply that factory ammo (which everyone points to as the standard anytime you’re having problems) would also cause this problem. As it is already at the spec to which I am bumping back to.

I guess the next step is to burn a bunch of factory ammo through it and measure the COAL every 20 rounds. See if it shortens things up. I really think that unbrunt powder is clogging this bitch up. I think a CCI 450 and 38.5 gr of Varget should burn fine behind a 87 VLD. But maybe not.

 

[Coyote Kev]

Somewhat of an update. I loaded some rounds with hornady brass and pretty much the same other components. Varget and Berger 87 VLDs. Obviously the primer was different. I used a CCI Br2. Anyway... I shot 72 times with those and a few other loads with Lapua brass and small rifle primers and had no measurable change in measured COAL. Although it’s too early to know, it’s pushing me toward the idea that I was getting incomplete burn of my Varget with a CCI 450.

 

[Coyote Kev]

I have now shot 170 rounds with no change in OAL. Then I cleaned the barrel and shot 30 rounds of Varget with Lapua brass and 40 rounds of hornady brass with H4350. I then measured the OAL with my 87 Bergers, and got 2.060 inches. I thought WTF? I then cleaned it and remeasured and got 2.220”. Which has always been my OAL with that bullet. So now I don’t know if I’m getting incomplete powder burn with small rifle primers in the Lapua brass or if it was the dirty as hell 4350 clogging shit up. I plan to shoot the Lapuas with CCI 450s and Varget exclusively and figure it out.

 

[Kopfjager1]

What's your buffer weight and buffer spring? It could also be that your extractor and or ejector spring is really heavy. Using a LMT 308 BCG and a too light of buffer spring caused this issue as well.

 

[Coyote Kev]

I have a 4.2 oz hydraulic buffer and I now run a sprinco extra heavy "orange" spring. I was running a tubbs flat wire spring but changed to get more closing force. I run a JP high pressure bolt that has a very heavy ejector spring, but how is that involved?

 

[Coyote Kev]

What's interesting is I shot 170 rounds of mostly large rifle primer brass with zero measurable change and then just 30 rounds of small rifle primer and the lands got all clogged with shit. The variable here is the large rifle primer brass and h4350. I shouldn't have shot that before I remeasured but sometimes when you're at the range u shoot what you got.

 

[Coyote Kev]

What's your buffer weight and buffer spring? It could also be that your extractor and or ejector spring is really heavy. Using a LMT 308 BCG and a too light of buffer spring caused this issue as well.

See above posts. Heavy ejector spring?

 

[Kopfjager1]

I have a 4.2 oz hydraulic buffer and I now run a sprinco extra heavy "orange" spring. I was running a tubbs flat wire spring but changed to get more closing force. I run a JP high pressure bolt that has a very heavy ejector spring, but how is that involved?

Apologize for the delay. With a combination of light buffer spring weight and the heavy ejector and and or extractor tension, it can prevent the cartridge from fully seating into the bolt. Had it happen once with improper AR10 Carbine buffer and the LMT 308 Enhanced BCG (2 extractor springs).

 

[Coyote Kev]

So I measured my OAL at the ogive of the 87 Berger VLD and it was the same as when measured new. I then went and shot 22 rounds of those bullets with Hornady brass, CCI 200s, and H4350. Had a couple chambering problems when I was close to done. Looked down the barrel and it was dirty as shit with what looks like unburned powder and now the OAL measures much shorter. Like 2 tenths shorter. What the hell is going on? Never had any of these problems with my JP 260. This 6 Creed has been nothing but problems.