lead deposits behind AR gas rings

[Brandon]

So I was wondering about leading in AR's. Now I know that this is a topic that has probably been beaten to death but I thought I'd ask aboout a specific. So My barrel doesn't seem to have leading that I can see anyway, but when doing a cleaning of the bolt carrier and bolt I notcied that there was lead near the back of the bolt when I disassebled the group. The lead deposit is just behind the gas rings of the bolt. I know with a harder lead and possibly a wider boolit (mine is the Lee 230 gr. .309) I might have better luck, but shouldn't I be seeing lead inside of the barrel also if it's on the bolt? And it makes me wonder what my gas tube looks like on the inside. Any suggestions would be very appreciated.

[popper]

Picture?
The lead deposit is just behind the gas rings of the bolt ? Toward the lug end of the rings? Li'l gun powder? I get carbon buildup but not Pb.

[petroid]

I had it early on after I got my barrel. After shooting more it stopped. I think there is/was probably a burr at the gas port that was causing lead to scrape off and get forced down the gas tube and deposit on the tail of the bolt. It hasn't happened again whether I am shooting naked lead or PC'd boolits.

[leadman]

Have you slugged the barrel? This would tell you if the is a burr or if the boolit catches in the gas port. You did not mention alloy but I recommend at least 18 bhn with 22 even better. This keeps the boolit from deforming in the bore and causing problems.
I shot some 11 bhn boolits with a full load in my M-1 carbine once and I did get lead shaving in the gas port and piston.

That boolit you are using is probably the worst design I have seen in my 40 years of casting. I did buy this mold when Midway first offered them. I tried many things to get it to shoot good and the only thing that made it work at all was installing a gas check on the boat-tail and shooting it in my Savage 30-06 at 1,800 fps to get 2 moa accuracy.

[Scharfschuetze]

That is a very common place for fouling to build up. Even ball ammo leaves a noticeable ring of hard powder fouling at that location and it can be very stubborn to remove. If your lead and lube for some reason is vaporized or shaved off, pressure in the barrel will force it into the tube, and if it makes it through the gas tube, that's one of the places for fouling to build up. It's natural to the M16/M4/AR15/AR10 impingement gas system. Clean to your satisfaction and expect to clean it again.

What is your load, alloy and velocity for the Lee 230 grain 30 cal boolit you are shooting? Am I correct in assuming that it is the one designed for the 300 Blackout (TL309-230-5R) with a plain base? Is it stabilizing in what I assume to be a 1 in 12" twist in your AR10?

[Brandon]

Quote - That is a very common place for fouling to build up. Even ball ammo leaves a noticeable ring of hard powder fouling at that location and it can be very stubborn to remove. If your lead and lube for some reason is vaporized or shaved off, pressure in the barrel will force it into the tube, and if it makes it through the gas tube, that's one of the places for fouling to build up. It's natural to the M16/M4/AR15/AR10 impingement gas system. Clean to your satisfaction and expect to clean it again.

What is your load, alloy and velocity for the Lee 230 grain 30 cal boolit you are shooting? Am I correct in assuming that it is the one designed for the 300 Blackout (TL309-230-5R) with a plain base? Is it stabilizing in what I assume to be a 1 in 12" twist in your AR10?[/QUOTE]

Correct, that is the boolit I'm shooting. Haven't installed gas checked any of them. Still just the stupid boat tail design. Haven't checked hardness but it can't be as hard as preferred. Using ww. My barrel is a 8" 1:10 twist 300 blk. I was using h110 and keeping them subsonic for a can. Anyone plugged up their gas tube yet? I tried pc but had horrible luck. I don't think I had them cooked long/hot enough. They left a big indentation when I seated them. Cooked at 400 for 25 min using Hf black which I hear sucks

[Scharfschuetze]

Brandon,

As you report no leading in your bore, it sounds like that plain base boolit is working in your rifle at your velocity. Out of curiosity, how is the accuracy? The blackouts that I've shot have had something like a 1 in 7 twist for heavy subsonic boolits, so I was also wondering if the 1 in 10 twist of your rifle can stabilize that long-for-bore boolit that you are using.

As far as the gas tube goes, they don't seem to get gummed up very often. The only time that I've seen them replaced was with extensive use of blanks while training in the Army and even then that was a fairly rare occurrence.

[Brandon]

I'm sorry I said 1:10 twist. Guess I was thinking of my .308. You are right it's 1:7. Accuracy is about like a pistol at 25 yards with subs. One inch at 25. Got less than 1.5 moa at 100 with a couple super loads. Better than an mp5 but still not as accurate as my 16" blk. It's a fun little pistol though

[Geezer in NH]

Wow many here are kind AR-15 and cast huh! what are you looking for?? DO not expect JK results. IN the ar15, casts are for practice cheap IMHO

[BD]

The rear of the bolt is the place where whatever vaporized solids which are in the gas stream condense. I've tried shooting plain base boolits in the .450B and always experienced poor accuracy and a very small amount of lead build up on the rear of the bolt. It is my belief that a plain base boolit allows a small bit of the base to be vaporized as it passes the gas port, leaving a notch in the base. I have never found any lead in the gas block or tube. Just that small build up on the bolt along with the carbon fouling.

[Brandon]

The rear of the bolt is the place where whatever vaporized solids which are in the gas stream condense. I've tried shooting plain base boolits in the .450B and always experienced poor accuracy and a very small amount of lead build up on the rear of the bolt. It is my belief that a plain base boolit allows a small bit of the base to be vaporized as it passes the gas port, leaving a notch in the base. I have never found any lead in the gas block or tube. Just that small build up on the bolt along with the carbon fouling.

Well that's good to know. I can clean a little lead off of the bolt occasionally if that is typically the only place you get buildup. Thanks