Bolt Teeth Broken

[TreeHugger]

I ordered it with barrel extension on and new from the factory. There were some pieces in the extension and most fell out of the upper. I'll check the headspace. Thanks!

Young manufacturing stated thst checking headspace for the bolt is almost uneccessary in an ar, since it is milspec, and that you would have a better chance at winning the lottery than the rifle blowing up on you. Some other top tier manufacturers also stated the same. My guess is that the bolt wss defective to begin with.

[m03]

See a few posts above re: Hydrogen Embrittlement. Have also seen this type of failure in the construction industry. Some structural bolts (A325 and A490) are hot dip galvanized, and if done wrong are noticably more brittle and prone to breakage. They break MUCH more easily when impacting them to torqe specs, compared to non plated bolts.

I'll concede the point in the instance of poorly manufactured bolts, which this one apparently was. It has everything to do with proper manufacturing and quality control, though.

My oldest son uses the M4 every day for the last 4 years at "work", and they do not have any trick coatings.

Cool story, assuming you don't consider parkerizing/phosphate a trick coating. There are plenty of examples of other military firearms with non-parked/non-phosphated bolts where you don't see the lugs shearing off (SCAR, AK47, etc). I don't seem to recall lugs breaking as being a major complaint of the early M16s either.

[kendog4570]

Kind of funny, when he was going thrugh Basic, they cleaned them so much that the phosphate was gone and you could eat off it, and now with his unit, they dont clean them to death, and leave a little carbon left in there for reliability.
Some folks he works with are using the scar and they like it, but the difference in the two guns is not significant enough to warrant the logistical nightmare of switching over.

[m03]

Some folks he works with are using the scar and they like it, but the difference in the two guns is not significant enough to warrant the logistical nightmare of switching over.

Not to get too far off-topic, but isn't it funny? They want something similar to what they already have, but as soon as those criteria are met, then it's too similar and therefore the change can't be justified.

They're waiting for something revolutionary, but arms development is all about evolution, not revolution.

[ott1]

The bolt is NiB coated and not hard chrome so it's not affected by Hydrogen embrittlement.

[SocomM4]

I'm loling at the people who are blaming a coating.
The reasons the Military doesn't use chromed or NiB BCGs are very simple,
1 cost,
2 they're shiny.


Military hates both.




It's just a bad bolt. End of speculation.

[send it_hit]

holy crap.

[BigCumfy]

Got my headspace gauge today as well as the replacement BCG and another one I purchased. The replacement looks exactly the same as the broken one, but just with the lugs attached. Checked headspace on the broken one and the BCG closed fully and was flush on the back of the upper. I then checked the replacement and the BCM BCG and both would not completely go into battery and was sticking out slightly out of the back of the upper. Is there any reason I shouldn't test the new BCG's out? If not, since I know headspace is good on both new BCG's, I will go to the range within the week and report back.

[ott1]

Take all of your parts to a qualified gunsmith to check headspace before you go to the range.

http://www.ar15.com/mobile/topic.html?b=3&f=4&t=315921

[Dirtbiker]

Got my headspace gauge today as well as the replacement BCG and another one I purchased. The replacement looks exactly the same as the broken one, but just with the lugs attached. Checked headspace on the broken one and the BCG closed fully and was flush on the back of the upper. I then checked the replacement and the BCM BCG and both would not completely go into battery and was sticking out slightly out of the back of the upper. Is there any reason I shouldn't test the new BCG's out? If not, since I know headspace is good on both new BCG's, I will go to the range within the week and report back.

What kind of gauge are you using? A GO, NO GO, or a FIELD?

[Cobrafreak]

The steel in your bolt was too hard (brittle) caused by improper heat treating. If you remove whats left of the bolt and put it on an anvil and whack it with a hammer it will break like glass. If this was a bolt action rifle it would have gone through your head and killed you. Get a MPI bolt and it won't happen like this. If you build your own rifle it's a good idea to have a GO and NO GO gauge. Brownells sells them and it will let you know without firing a round that your head space is within safe specs.

[BigCumfy]

Field Gauge.

[kendog4570]

Take all of your parts to a qualified gunsmith to check headspace before you go to the range...

That's some good advice.

[BigCumfy]

That's some good advice.

Agreed!

[mdib870]

your bolt proly rotated by the force of recoil your bolt teeth to slam into your locking lugs which proly caused your bolt to fail thats my guess