Bolt Carrier Group Stress Test

BY Herschel Smith
6 years, 1 month ago

This is an interesting video.  It wasn’t made to test the gun so much, but rather the BCG.  He makes that very clear.

It sort of makes you wonder about those Soldiers complaining about firing 400 rounds through their Colt guns at Wanat and Kamdesh only to see their guns seize up.

First of all, remember that the Army hasn’t trained their men in fire control and marksmanship like the Marines.  I’m not saying that – an experienced trainer who has time in Afghanistan is saying that.

Second, I maintain that the problems at Wanat had to do with being deployed at the bottom of a valley in between mountains, giving up the high ground, no logistics, no support, a poorly connected and poorly manned observation post, and a total time of more than a year from start to finish to build and man the COP (giving the Haqqani network time to deploy fighters at will).  Again, see multiple entries on The Battle of Wanat.  If you haven’t studied it, it’s a sad but necessary tale.

There is a rich history of blaming the gun for the failures when the real blame had to do with leadership, so it’s entirely misplaced blame to point to the gun.  But it does cause you to wonder if those Colt guns had a better BCG would they have seized up after 400 rounds (400 rounds in 30 or so minutes at Wanat).

There are a lot of very good coated BCGs like this Titanium Nitride component.  This is the guts of the gun.  It makes sense to outfit yours with a good one.



  1. On January 12, 2018 at 9:12 am, Pat Hines said:

    That’s why I have a FailZero BCG in my AR-pistol.

  2. On January 12, 2018 at 10:46 am, Pat Hines said:

    I went to AIM Surplus to check out that TiN coated BCG and saw that they also offer a NiB, nickel-boron, coated BCG for the same price. That’s what FailZero uses on their bolts. I don’t know which company has the superior product, but the AIM NiB BCG is a steal at $119.00, if it’s a good product.

  3. On January 12, 2018 at 11:40 am, Rocky Mtn Yankee said:

    Interesting to see the titanium nitride. I just recently switched back to a phosphate BCG from a nickel boron BCG (from DSG Arms) that I put about 3000 rounds through. After that many rounds, the NiB coating had become burnished and the “slickness” was gone. The last few cleaning sessions took considerably longer and more brushing effort with the burnished NiB BCG then with a phosphated BCG from a different rifle.

    I might have to give the Aimsurplus BCG a try since I do NOT recommend NiB.

  4. On January 12, 2018 at 12:15 pm, Herschel Smith said:

    @Pat and Yankee,

    Yea, this is something I need to study more and would like to see stress tests and reports on. Ni is a soft metal, Titanium is not. The BCG needs to slide freely in order to minimize wear, while it needs to be hard in order to maintain tolerance.

    I would also like to see good research into lubricants. I’d like to see more research into the use of lubes that bead into very small balls that act as bearings.

    Runners can get things like that to prevent chaffing. Why can’t we design one [a GOOD one] for high stress and high temperatures, thus adding to the life and reliability of the BCG?

  5. On January 12, 2018 at 1:18 pm, ambiguousfrog said:

    Have a 5.56 lwrc with NiB bcg. After 180 rds. I didn’t like the burnt or discoloring of the NiB assembly upon first cleaning. In an odd location too, at the rear of one side of the carrier. According to others on their community forum, it’s normal. I just don’t have enough experience with these coatings and what is the norm. To me it looked more like a heat thing than a dirt thing.

    Per one comment:

    Part of the discoloration is the way the NiB surface is. It’s not “flat” more of microscopic ridges which is why it feels slick. The gaps between the ridges can collect dirt, oil, etc. doesn’t effect function.

  6. On January 12, 2018 at 2:04 pm, Angus McThag said:

    I assume you’ve seen Colt’s test with an M4A1(pre-SOCOM barrel) firing cyclic on a test fixture?

  7. On January 14, 2018 at 10:01 am, Heywood said:

    @Pat. So you have been really happy with the Failzero? I haven’t heard from any “real” users on how they work.

  8. On January 14, 2018 at 11:40 am, george said:

    In 1988 at the M16 Instructors’ School we had one day where we fired 1200 rounds without cleaning. When the guns started to slow down their cycling we would squirt more Break Free CLP into the two holes on the bolt carrier. They were nasty dirty by end of the training cycle that day, but they kept running. CLP is no longer the lube to go to, but as long as they stay lubed they should run. (Those were Colt M16s)

  9. On January 14, 2018 at 12:02 pm, Matthew Wilbanks said:

    +1 George

    Also if anyone wants a crash course on why an AR is built the way it is, what makes it run, what makes it choke and the processes that go into their manufacturing, watch these two videos.

    Herschel has post plenty of good info along these lines, but the 7+ hours of total content in these videos will slay a lot of sacred cows and piss off tons of Arfcom members.

    I don’t have any experience with the Nickel Boron or Titanium Nitride coated BCG’s, but I typically use your standard salt bath nitride (Melonite) finished ones. It’s a huge advancement over phosphate, slick as snot and durable to boot. I’ve heard NiB and TiNi are better still, but they typically cost 50-100% more. Standard nitride is pretty much the same cost as phosphate.

    I’ve also switched over to using nitride barrels as they are much more resistant to rust on the outside. In the bore, the nitride provides much the same wear resistance that chrome lined bores used to, without the extra cost or more limited life span.

  10. On January 14, 2018 at 1:25 pm, moe mensale said:

    “But it does cause you to wonder if those Colt guns had a better BCG would they have seized up after 400 rounds (400 rounds in 30 or so minutes at Wanat).”

    If my math is correct, that’s 13.3 rounds per minute. The sustained rate of fire for M16/M4 weapons is 12-15 rounds per minute. The factory Colt BCG doesn’t appear to be the main culprit here.

  11. On January 14, 2018 at 2:37 pm, Matthew Wilbanks said:

    Moe, yup the standard failure point of an M16 on full auto or very rapid fire is usually between 400-500 rounds. The guys at IraqVeteran8888 on Youtube have done multiple M16 “meltdown” videos with uppers of varying quality, and the gas tube usually melts and gives out in that range.

    Some crappy uppers have only made it to the 300+ range and I think one of the better ones they tested made it to 600 or so.

    You occasionally also get barrel droop on bad quality or pencil barrels. I don’t recall them having any hard failures due to fouling buildup, but once you’re at the upper end of that range it will cause FTF/FTE.

    It’s an infantry rifle, not a squad automatic weapon or light machine gun.

  12. On January 14, 2018 at 10:29 pm, Herschel Smith said:

    But Moe, think about what you’re saying. If that’s the spec rate of fire, and the guys at Wanat didn’t exceed it yet their guns still failed, then some component failed even though it didn’t exceed spec.

    That’s the point. I still suspect it was the BCG.

  13. On January 15, 2018 at 12:17 pm, moe mensale said:

    “That’s the point. I still suspect it was the BCG.”

    The BCG is a pretty robust assembly of parts. It’s basically the heart of the gun and I would think not being normally prone to early failure. Unlike the gas tube which is a sacrificial component. Of course, anything man-made can break at any time. I don’t know enough about the Wanat battle except to say in my opinion there was a fatal combination of mechanical and human failures and errors.

    This reminds me of the M16 fiasco when first used in Vietnam. Eugene Stoner’s design wasn’t the problem. It was primarily the bureaucrats’ screwing around with the ammo specs and thinking it was a self-cleaning system.

  14. On January 15, 2018 at 12:21 pm, Herschel Smith said:

    Well, the gas tube is certainly a possibility. What I would like to have seen is a full forensic analysis of those guns post-mortem by someone other than Army armorers. They should have sent them to the gunsmiths at Hyatt Gun Shop and let those guys write a report on it. Then we’d know.

  15. On April 28, 2018 at 12:59 am, Georgiaboy61 said:

    Re: “This reminds me of the M16 fiasco when first used in Vietnam. Eugene Stoner’s design wasn’t the problem. It was primarily the bureaucrats’ screwing around with the ammo specs and thinking it was a self-cleaning system.”

    Although the AR15/M16 is a direct gas-impingement design, which channels hot gas and fouling back into the bolt-BCG, that has not been the sole reason for failures in the field. Over the years since Vietnam, and the disastrous introduction of the weapon, the main reliability issues seem to be related to feeding (especially poor magazine design/construction – now largely resolved), extraction and ejection. Some users have also has issues with buffer springs not being robust enough.

    Fifty years is a long time to sort out technical problems, and for the most part, time and lots of effort by different specialists and experts over the years has turned this family of rifles/carbines into an excellent platform – one reason why so many tier one types use it. But let’s no pretend that it has been cheap, or easy.

    Stoner’s design was superb in many respects, ahead of its time really – not only the AR15, but the Ar10 which preceded it. The AR15 wasn’t perfect, though, far from it. Stoner erred in designing a rifle which would run reliably using only a specific propellant and weight of bullet.

    As John C. Garand before him had learned, the Army Ordnance Dept., the Navy, the Marine Corps, etc. all had their own ideas about how best to use their rifles – and that included changes/alterations of the ammunition. Garand had designed his M-1 to work using 173-grain FMJ (M1 Ball), which was adopted in 1926. However, in the 1930s, the Army adopted M2 Ball (FMJ), which was 147-150-grains in weight. Garand had to scramble a bit, but ultimately his design proved robust-enough to work with the new cartridge.

    Eugene Stoner should have foreseen that the ordnance department and the respective services were probably going to make changes in his original specifications at some point, and designed in enough flexibility to account for this. Ammunition manufacturers, for example, alter their propellant formulations all the time – sometimes more or less inadvertently as a natural result of variances in different lots of powders made for bulk contracts. That doesn’t even take into account unforeseen changes in propellants made due to shortages and other causes.

    When the change was made from stick (extruded) powder to ball powder, it threw the carefully-timed operation firing cycle of the weapon totally out-of-whack. The rate of fire when used on fully-automatic, increased dramatically; overstressed buffer springs and other parts began to fail, not only because of the increased physical stress but due to dramatically elevated fouling and significant heat buildup.

    Stoner was right to protest these unauthorized changes to the ammunition, but he was wrong not to have foreseen this and built a bit more robustness and adaptability into his design.

    Another failure was the lack of chrome plating for the bore, chamber and bolt-BCG. The lack of chrome plating only compounded the idiotic decision not to supply cleaning kits with the new rifles. What genius at the Pentagon/DOD thought that one up?

    AR15s/M16s/M4s are all superb weapons, but analogous to a Swiss Watch or a Ferrari. They have to be maintained properly and tuned to keep them running; they don’t stand neglect well. The AK47, on the other hand, is analogous to a Chevy – it isn’t as easy to use or as well thought out as an AR15 (nor as accurate), but like your basic Chevrolet, it is serviceable, tough-enough to withstand abuse, and gets the job done.

    I suppose what I am saying is that for all his genius, Eugene Stoner didn’t make a weapon designed to be “soldier proof,” whereas Mikhail Kalashnikov did.

    The late Colonel David L. Hackworth, one of the best soldiers our nation has produced, and a man renowned as a guerilla fighter in Vietnam, hated the M16 and was fond of telling his troops that the Ak47 was a real infantryman’s weapon – which he would then demonstrate by digging one up, clearing the mud and debris from the barrel – and then without any further cleaning whatsoever – fire a full 30-round magazine without any issue whatsoever.

    Obviously, the AR15/M16 family of weapons has come a long way since Vietnam, but the comparison still stands. Americans often ridicule Russian weapons designs, but if we were smart, we’d study them with the respect and attention they deserve – for that nation has a long and successful track record of designing robust, tough and effective weapons which get the job done even under the worst conditions.

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You are currently reading "Bolt Carrier Group Stress Test", entry #18427 on The Captain's Journal.

This article is filed under the category(s) AR-15s,Firearms,Guns and was published January 11th, 2018 by Herschel Smith.

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