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AR-10 T rapid shooting,,

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11 years 11 months ago #14552 by LebbenB
Replied by LebbenB on topic AR-10 T rapid shooting,,
Welcome to the site and thanks for your service. Also, congrats for making it out of Asscrackistan safely.

The SF bubba was essentially correct. Rapid, repeated strings of fire are hard on AR bolts. Not just AR10 bolts - ALL AR bolts. The Army says the average lifespan of an M4 bolt is 7-10,000 rounds. (My reference for that number is the -30 level maintenance manual for the M16 FOW. Get with your BSB guys and see if they've got one lying around. Remember - you're an 11B and you have sticky fingers, LOL)

Common points of failure are sheared locking lugs and breakage at the cam pin hole. Armalite mitigates the sheared locking lugs by beveling and relieving the 6 o'clock lug on the bolt. This allows for a more uniform distribultion of pressure on the rest of the lugs

Read more about it here: www.armalite.com/images/Tech%20Notes/Tec...%20Bolt%20960507.pdf

AFAIK, there's no "fix" for a bolt breaking at the cam pin. It's just the nature of the beast.
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11 years 11 months ago #14554 by LebbenB
Replied by LebbenB on topic AR-10 T rapid shooting,,
Ref Carbine uppers on "rifle" lowers: Armalite carbines have a mid length gas system, so the rifle sized buffer/buffer spring shouldn't present a cycling problem. Replacing a fixed buttstock with a collapsible unit is not as simple as it sounds.

Be careful when pulling the fixed stock off. The spring and detent for the rear takedown pin is held in place by the stock. You will then need to remove the receiver extension (buffer tube). Do this carefully because the receiver extentsion holds the buffer detent in place and it's spring loaded. You then must re-install the receiver extension along with a lower receiver plate and castle nut. This will allow you to use an adjustable stock like the Magpul UBR or the Ergo F93. Should you want to use a buttstock like a Vltor or Magpul CTR, MOE, et al, you'll need to replace the original rifle length RE with a carbine length M4-type unit. This means you'll need to replace the buffer/buffer spring with a carbine weight buffer and carbine length spring.
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11 years 11 months ago #14572 by 13fcolt
Replied by 13fcolt on topic AR-10 T rapid shooting,,
I really thought the round count on the bolt (M4) was something like 50-60k? Naturally, I can't find that reference, but I was sure of it.

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11 years 11 months ago #14585 by LebbenB
Replied by LebbenB on topic AR-10 T rapid shooting,,
The average M4 bolt will start to crack around 5K with visible cracks around 7-10K. Once cracks are visible to the naked eye, the bolt should be replaced. ALWAYS check the headspace of the barrel prior to doing this.

At the beginning of 2012, the US Army announced a PiP for a longer wearing M4 bolt. PEO Soldier was looking for something like 25% improvement over the durability of the current Colt bolt. The program was cancelled last summer when the submitted bolts didn't offer a great enough improvement over the current bolt to justify the increased expense of the bolts.

.308 Rifle/Midlength gas systems (Like Armalite's) are easier on bolts than a carbine length gas system due to the softer gas impulse. I really wouldn't worry about bolt breakage until it happens. I keep and recommend users have a spare bolt on hand, just in case.

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11 years 11 months ago - 11 years 11 months ago #14586 by jtallen83
Replied by jtallen83 on topic AR-10 T rapid shooting,,
Is there a round count that will void the Armalite lifetime guarantee? I planned on shooting the crap out of mine and sending it in for warranty repair if my bolt or anything else cracks.
Last edit: 11 years 11 months ago by jtallen83.

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11 years 11 months ago - 11 years 11 months ago #14587 by 13fcolt
Replied by 13fcolt on topic AR-10 T rapid shooting,,
This is good to know. I do still have the bolt from one of my first AR15 around some where that is well past the 30k mark. I think I'll dig it up and have a closer look. My current AR15 has the LMT enhanced bolt, which has the shaved lug opposite the extractor, it's sitting around 8k right now. With all the hand me down weapons I used in the army, and unknown round counts, I've only ever seen a bolt break in a 249, but that's a different animal.

Would heat from the high fire rates have more to do with accelerated wear, as opposed to what a civy weapon would see?
Last edit: 11 years 11 months ago by 13fcolt.

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11 years 11 months ago #14604 by LebbenB
Replied by LebbenB on topic AR-10 T rapid shooting,,
JT - No, I don't think Armalite has given out a precise round count that voids the warranty

With all the hand me down weapons I used in the army, and unknown round counts, I've only ever seen a bolt break in a 249, but that's a different animal.

There it is. My experience was much the same, though I did have a bolt break on me while training at Moyock, NC. I didn't realize it til after the day's training was over and I was wiping it down for turn-in back at Bragg.

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