Broken or cracked USGI Carbine Bolt

[Bruce McAskill]

It was common on the type 1 bolts that an engineering change made the extractor pocket a wee bit stronger in the type 2 bolt. But they can still break and many times from the bolt not closing all the way because of a case being just a tad to long. The pockets the lugs rest in the receiver can become damaged over time. This will hold the bolt back just enough time to cause the bolt to be slammed causing extra pressure to be brought against the right side lug and breaking the lug in the extractor area. The type 3 bolt aka round bolt ( and not the name M2 bolt as it was in use well before the M2 carbines came along.) is still a bit stronger but they too have been know to let go now and then. If one reloads then DON'T push the rounds to the very peak of speed. Standard loads work fine and a 75+ year old carbine will still preform fine. All makers of the typ1,2 and 3 bolts have had breakage. I had a very early Underwood bolt break on me with factory ammo. No reason for it except it was just an early type 2.

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[DaveHH]

Bruce covered everything that causes the bolt failure. One thing to know, I seem to recall this coming from BQ, if the failure is a result of a problem with the receiver (damaged slots on the left side, beat up receiver lugs etc.) the carbine will continue to break bolts one after another.
Additionally, the carbine has an Achilles heel, it is cartridge case length. If the case is too long, the bolt will never close all the way. During the manufacture of the 6M carbines, carbines were blowing up at an unacceptable rate. The problem was solved by measuring 100% of ammunition cases. I would check on your ammunition and headspace the weapon.