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Posted: 9/2/2013 12:30:38 PM EDT
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For years I’ve heard all about this and that about not shooting cast bullets in direct impingement rifles; mostly about clogging the gas tube. Until recently I never had a problem with cast bullets other than leading of rougher barrels like on my LAR 50 or my super Blackhawk.. I was shooting bullets cast from wheel weights through my 300 whisper when I started having bolt sticking problems in and out of battery. I thought it was related to the excessive fouling from the bullet lube while shooting suppressed but the problem remained after cleaning the bolt face and barrel adaptor.
My usual cleaning routine for my AR-15’s running a bore snake down the barrel, wiping down the receiver interior and cleaning the outside of the bolt carrier and bolt. It wasn’t until I finally took a look at the interior of the bolt carrier that I found a large lump of lead and other fouling about 180 degrees around the back of the carrier interior which was causing the bolt to stick inside of the carrier. I guess I never thought about where the gas from the tube went when it entered the gas key. It seems enough lead vapor from 300 rounds of cast 300 whisper entered the area inside of the carrier behind the bolt gas rings and condensed into a solid lump that I had to chisel off with a small file. So why does the gas key allow gases into the back of the bolt? Is it to keep the bolt locked shut long enough to prevent barrel gases from blow torching out of the ejection port? If I clean out the bolt carrier every 50 rounds will this keep things from jamming up? I think I’ll buy some bulk spire point flat base bullets (150 grain boat tails suck when subsonic) as a cheaper alternative to Sierra 240 hpbt but until then I’ll use the 230 grain cast. Ranb |
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I think I’ll buy some bulk spire point flat base bullets (150 grain boat tails suck when subsonic) as a cheaper alternative to Sierra 240 hpbt but until then I’ll use the 230 grain cast. Quoted:
Do you really shoot cast lead bullets in an AR? Amazing! I'm surprised any serviceable lead actually makes it out of the barrel. Any muzzle velocities greater than about 2000 FPS will pretty much destroy the bullet. Not sure why you think that. The cast bullets I'm using are 230 grain at 1060 fps. No leading of the bore that I can see at all. I use lead in my 458 socom; 500 grain subsonic with gas checks, no lead problems in that bolt carrier or bore at all. Ranb |
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Do you really shoot cast lead bullets in an AR? Amazing! I'm surprised any serviceable lead actually makes it out of the barrel. Any muzzle velocities greater than about 2000 FPS will pretty much destroy the bullet. People push gas checked cast ballots faster than 2000 using an appropriate hardness alloy. |
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So why does the gas key allow gases into the back of the bolt? Is it to keep the bolt locked shut long enough to prevent barrel gases from blow torching out of the ejection port? TECHNICAL NOTE 50: THE CYCLE OF OPERATION AS A GUIDE TO TROUBLESHOOTING http://www.armalite.com/images/Tech%20Notes/Tech%20Note%2050,%20The%20Cycle%20of%20Operation%20as%20a%20Guide%20to%20Diagnos….pdf This tech note has illustrations to show what happens; when the bullet passes the gas port; a metered amount of gas goes back into the gas key, and into the carrier. The gas pushes the carrier back, and while doing so the gas pressure pushes against the backside of the bolt, unlocking it. As it unlocks it extracts the spent casing, cocks the hammer, ejects the spent casing, and then loads another round into the chamber. |
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People push gas checked cast ballots faster than 2000 using an appropriate hardness alloy. Quoted:
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Do you really shoot cast lead bullets in an AR? Amazing! I'm surprised any serviceable lead actually makes it out of the barrel. Any muzzle velocities greater than about 2000 FPS will pretty much destroy the bullet. People push gas checked cast ballots faster than 2000 using an appropriate hardness alloy. Powder coat them. 
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I doubt that solution will damage steel. Might smell a bit funky though.
Here give this a read, powder coated cast bullets Understandably cast bullets are fine in a semi auto. There will be a small amount of lead particles that pass into the action, and as you noticed they will eventually build up. They can also be a pain to completely remove, just like barrel fouling/leading can be a PITA. |
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Quoted: So why does the gas key allow gases into the back of the bolt? Is it to keep the bolt locked shut long enough to prevent barrel gases from blow torching out of the ejection port?  it pushes the bcg back, which cycles the round |
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uh that's how the piston operates.
it pushes the bcg back, which cycles the round Quoted:
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So why does the gas key allow gases into the back of the bolt? Is it to keep the bolt locked shut long enough to prevent barrel gases from blow torching out of the ejection port?
it pushes the bcg back, which cycles the round I knew that the bolt carrier was pushed back by the gases. I thought the bolt carrier merely moved back forcing the cam to rotate the bolt until it unlocked and continued back along with the carrier. I didn't know the gases also acted directly on the bolt by pushing against the back of it while also pushing back on the carrier. Page ten of this link shows what I was missing. Evaluation of gas systems for the AR-15 I never really thought much about why there were gas rings on the bolt. This is one of those duh moments I guess. :) Ranb |
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I think this sentence will lead you to your answer. I think you need to harden up that lead. Quoted:
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I was shooting bullets cast from wheel weights through my 300 whisper when I started having bolt sticking problems in and out of battery. I think this sentence will lead you to your answer. I think you need to harden up that lead. Wheel weights aren't as hard as linotype, but they do have some tin and antimony in them already; they are harder than pure lead. I don't have this problem with my 458 socom, probably because I'm using gas checks and the back of the bullet is somewhat protected. I'm not getting any lead sticking to the bore that I can see while cleaning. Ranb |
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To clean the lead and/or carbon from the bolt and carrier, buy a C.A.T. 4 or Otis B.O.N.E. carbon scraper tool.
These tools will clean leading or carbon from the bolt "tail", the inside of the bolt carrier, and from the front side of the firing pin flange. You can also use a carbon and lead removal chemical like Slip 2000 Carbon Killer. Soak the bolt and carrier for 15 minutes then brush with an M16 toothbrush. As above, to shoot lead bullets at rifle velocities you need to put gas checks on the bullets. |
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yes Quoted:
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Will immersing the bolt in the vinegar/peroxide dip damage it? Ranb yes is correct. OP: I've shot cast bullets for years in pistol, revolver and rifle and killed game and varmints with them. But never with the AR. Not saying I wouldn't, but I just never have. There is one more issue you might want to work thru. That is the production of lead particulate in the gas being sent back into the action and your propensity to breath it in while shooting. It is known that the high heat and pressure caused by combustion of the powder will melt the rear of a cast bullet AND produce lead vapor to boot. This vapor then mixes with the gases of combustion, enters the gas tube and gets sent back to the action. In so-called "piston" guns this is not too much of a problem as the exterior piston acts as a block to prevent inhallation of direct lead and other toxic fumes. No so with the AR internal piston. That "smoke" that comes out of the receiver includes lead vapour and particulate. The lead fouling is merely a portion of it stuck inside the action. I would think that in a suppressed gun this would be worse than unsuppressed due to the longer total time there is resistance of gasses on the base of the bullet with concomittant forcing of the gases back inside the gas tube. Yes, I am thinking gas-check bullets would be best, at least. As for shooting wheelweights at 2000 fps. As you already know, yeah, it can be done and is all the time using pretty basic lubes with little or know leading. |
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