Every time you shoot, clean the bolt and inspect it. When you see a crack replace it.
You will see a crack with the naked eye long before it becomes dangerous.
In a test, they actually cut off the two lugs that normally fail first, the two either side of the extractor and shot them. The two bolts lasted 720 and 1800 rounds before the guns failed the NO-GO headspace measurement and they stopped. Note that is the NO-GO, not the FIELD gauge.
I'm curious what the original source of this information is from? This here is saying that the bolt life difference between a carbine gas M4 and rifle gas M16 is not too different, which seems to run counter to everything else I've read, especially with reports of M4 bolts breaking more frequently than M16 bolts.
Or was just from that particular era of M4s from Colt (early to mid 2000s) that had quality control issues with the bolts?
Last edited by ta0117; 05-20-21 at 11:04.
Good thread . Subscribed.
Certainly could use anything near that kind of discussion volume. Maybe I wouldn't have to see constant references to "see this and that on TOS" which is code for "the info you're after is on www.ar15.com go there instead"
That is why I joined this place and not the other one, folks hear are friggin knowledgeable. I will admit I am a newbie to the AR even tho I have had a AR for 22 years! I was more into pistol shooting and training. I have learned more hear in the past couple months than the past year lurking around the other site.
I'm probably going to ask some stupid ass questions & if I do I am just trying to learn something. I really like this site. 🙂
Last edited by Spooky1; 05-20-21 at 23:06.
The data came from "System Assessment for PEO Soldier Reliability and Dust Assessment for the M4, M16, and M249," U.S. Army Evaluation Center, January 2007
This test was redone in 2015 to re-baseline these weapon systems with the new M855A1 with the results published in "Final Report for the 2015 Re-Baselind Reliability Test 5.56mm Weapons Using M855A1," Aberdeen Proving Grounds, August 2016.
The expected bolt life from both tests is around 10,000 to 12,000 rounds MRBR, M16 bolt 13,000 to 15,000 MRBR.
There are a number of reports that substantiate this, test where 10,000 to 12,000 rounds are fired in a number of M16s or M4s, and they do not require bolt replacement during the test.
What I have not run across is any scientific study that supports the 5,000 round bolt life.
Last edited by lysander; 05-21-21 at 09:21.
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