Bolt carrier group replacement

woodnut

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I have an AR 10 with an Armalite bolt carrier group. The builder liked that brand because of the spring on the firing pin. Said it would lessen primer hits as the bolt closed and "slam fires".
Now, it has been doing very well with 95 and lighter bullets; but when I started trying 108s and a VERY mild load, I got pierced 7 1/2 primers! Not once, but four in a row! I quit at that point. Load worked very well in my bolt rifle and was a low starting load of H4350.
I am just wondering IF my firing pin is going too long and maybe getting a new bolt carrier group might be advisable. But can you just order a group for an AR10(and 15 for that matter) and just replace? Are they made with tight enough tolerances to keep headspace correct? Any thoughts would be greatly appreciated!
 

PBramble

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You can order BCGs for them. The headspacing is set off of the barrel extension.
 

woodnut

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I thought so! Thank you for confirming it. I didn't know exactly how the headspacing was done, only assumed. I'm also thinking it won't matter which brand of BCG I order?
Right? Armalite or some other won't matter?
 

PBramble

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First, I'd check the firing pin. Look for proper protrusion depth and make sure there is no wear (burrs, nicks, etc.). Check for debris in the firing pin hole, this can make your pin hang up. If it's a no go, I'd order a new pin first.
 

sedancowboy

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I would not just order a BCG and expect it to fit in your gun. Depending on the age of your gun a lot of things can change with wear. Armalite will insist that you send in your bolt so they can headspace it if you have them do any work to your rifle. If you do order a new BCG then you should by all means check the head space. Only Armalite BCG will fit in my Armalite guns. The bolt locking into the Barrel extension is what sets the head space.
 

woodnut

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sedancowboy, (now that's an interesting handle!), I like what you say. That seals it, I will order an Armalite BCG. What makes me think it is the BCG causing the problem to arise when going to 108s is that the orginal BCG was lost by a dealer who was going to put a hard coat on it. He provided a done BCG , but I can't be sure it is an Armalite. Only the firing pin is for sure an Armalite. I'm 99%, but not 100% and there lies the question: is it or not and is it the cause?
 

Laelkhunter

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Have you tried any other brand of primers? Just wondering if it could be the Remington Primers, even though they were fine with the other loads. Was there any other sign of excessive pressure or just the pierced primer? I understand you wanting to be cautious with the loads.
 

woodnut

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Good question, Laelkhunter, and no, I have way too many 7 1/2s to want to try another. But...maybe I should. A lot of folks choose the CCI 450s and I think the BR4s would make a better choice of those two just by reading all the dimensions of each, along with those of the 7 1/2s. Not a bad idea! I could still use my 7 1/2s in other cartridges.
I actually have had 7 1/2s in other cartridges to be pierced. I know they were hot loads, though. And almost always in one of my ARs. As to other pressure signs, none. No bulges, no hard bolt lift, no stretching,etc. in any of the piercings.
 

Laelkhunter

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Might be cheaper to try another brand of primer than to spend the $$ on another bolt carrier only to find out that it wasn't the problem. Good Luck !!
 
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