16” midlength vs 20” rifle length bolt life

[Firefly]

I think so.

Years ago, when I built an AR for 3-gun matches, I went with an 18" rifle length gas tube.

It shoots very soft

That’s hot. All of it. Is that Bushmaster lower?

[lysander]

Back when I was new to the forum I tried to get the people who called themselves experts or professionals or insiders to tell me what an appropriate preventative maintenance schedule on a bolt in a carbine gas 16" would be.

I never could get an answer out of anybody. Just "until it breaks there's no such thing as PM on a rifle" or "you won't get there".

Have things changed?

Is there some kind of a guideline or consensus on how long a "it has to work" bolt in a high stress application should be trusted?

Let's say my run of the mill BCM bolt in a suppressed SBR running full power 5.56 with an oversize BCM gas port that operates violently. How many rounds till you (anybody) would go ahead and swap that bolt?

Or is it still "you can't break an AR15 bolt"?

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.

[ta0117]

There was a long and detailed discussion about bolt life in the following thread from last year. You may have missed it. lysander posted some really good data (which I assume is true) in that thread.

I posted in my thoughts in that thread. There are lots of different perspectives on the issue.

"When is a bolt "old"?"
https://www.m4carbine.net/showthread...-quot-old-quot

Hope this helps.

Joe Mamma

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?

[202]

Good thread…. Subscribed.

[fedupflyer]

Good thread…. Subscribed.

Are you effin kidding me...this place is turning in ARF dot com

[Warp]

Are you effin kidding me...this place is turning in ARF dot com

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"

[202]

Are you effin kidding me...this place is turning in ARF dot com

Come on! Isn’t that why we are all here? To share some knowledge.

[Spooky1]

Come on! Isn’t that why we are all here? To share some knowledge.

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. 🙂

[lysander]

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?

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.

[okie]

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.

Who said 5k, and what weapon? Mk18?