Has anyone experienced a broken bolt or sheared lug?

[Sry0fcr]

What gas system were you using?

[Chubbs103]

Someone 2 places down the firing line from me sheared a lug one day. Standard M4A1. As issued (carbine length gas system). M855A1 ammo. Lug that sheared was adjacent to the extractor. For what it is worth, the RO stated he has seen more sheared lugs since the introduction of M855A1.

[1168]

Seen a few on M4a1’s. With regular green tip. Usually discovered when cleaning.

Edit: lugs.

[vicious_cb]

Yes, but both times the bolt was defective to begin with. All of my Colt or BCM bolts lasted the life of the barrel no matter the gas system. Lesson: buy a quality bolt.

[sinister]

Broke the bolt on a student M4A1 at Fort Bragg at a shooting course. Bolt sheared at the cam pin hole.

That carbine had so many rounds through it the bird cage had extreme flame-cutting on the down-range side of each of the compensator slots.

[morpheus562]

I saw a few bolts break on M16s and M4s while I was an XO for a basic training company. Healthy diet of M855 green tip ammo, and the rifles were abused by the privates. I remember one sheared lug jammed up a gun during rifle zeroing. With the consistent rounds these guns received along with lack of maintenance, I'm not surprised.

I was cleaning my wife's BCM rifle last night (14.5 mid length) and saw one of the bolt lugs was chipped. Put in an order for a new one and will be swapping it out.

IMG_20200327_221318.jpg

[MegademiC]

Gas system length is one of many factors that contribute to a broken lug

These factors would include:
Round count
Bolt coating
Coating method and post-treatments
Gas system length
Ammo
Gas port size
Dimensions
Heat treatment (was it done properly?)
Shot peening
Base metal chemistry
Inclusions
Rate of fire

*a lot of these interact and Im sure Im missing some, this is just off the top of my head.

If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.

[Sry0fcr]

Gas system length is one of many factors that contribute to a broken lug

These factors would include:
Round count
Bolt coating
Coating method and post-treatments
Gas system length
Ammo
Gas port size
Dimensions
Heat treatment (was it done properly?)
Shot peening
Base metal chemistry
Inclusions
Rate of fire

*a lot of these interact and Im sure Im missing some, this is just off the top of my head.

If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.

I understand that this isn't scientific. I'm just trying to get a general picture whether or not people are/were/have experienced some of the common issues attributed to the violence of the carbine gas system in other gas systems. Or if some of the advances (LMT enhanced BCG, KAC E3) are rendered mostly moot if you're no longer running a carbine gas system.

[mack7.62]

Gas system length is one of many factors that contribute to a broken lug

These factors would include:
Round count
Bolt coating
Coating method and post-treatments
Gas system length
Ammo
Gas port size
Dimensions
Heat treatment (was it done properly?)
Shot peening
Base metal chemistry
Inclusions
Rate of fire

*a lot of these interact and Im sure Im missing some, this is just off the top of my head.

If someone had a sheared lug, and what gas system is, by itself, worthless info IMO.

You forgot firing a proof round, according to Knight's that cuts the bolt life in half, KAC skips that and warranties their bolts for 22,000 rounds.

[ace4059]

I’ve had a few chips on carbines and mid lengths and only found one lug cracked. A small chip doesn’t bother me but I keep an eye on it. Multiple chips and crack gets a replacement. They can fail at any round count but the few I have replaced saw about 10,000 rounds. There are too many factors to predict when it will fail.
Remember, just because a lug shears doesn’t mean you are out of the fight. The gun can still work perfectly missing a lug. If I was in combat and one happened to shear, #1. I Probably wouldn’t know right then, #2. I Wouldn’t care even if I did know and keep shooting.
Im not doubting Morpheus562 has seen a gun lock up due to the sheared lug... I’ve had some lock up due to hot ammo blowing a primer and it getting lodged in the FCG. It’s always a chance with anything happening with a machine and something can cause a jam.
Always use your best judgment.
Be aware I’m not advocating to keep using a rifle with a sheared lug, But lots of times one will break and the person doesn’t notice until they clean the rifle later on.
Make inspecting the bolt part of your cleaning process and check headspace when you replace the bolt.
Stay safe out there.
-Ryan