Weekend Inland Mishap

[American Patrol]

I took my mixmaster inland out to the desert last Saturday. After shooting the gun about 30 times the oprod-side bolt lug sheared off spilling the extractor and ejector w/spring stayed in the mag. well. The receiver and stock was not damaged at all. My son who was shooting at the time was not injured.

We were using CMP Aguilla (sp?) ammo and the gun was in really nice condition and I have shot it many times before without mishap.

Has this ever happened to anyone else? Is aguilla ammo very high pressure? I am looking for a nice condition bolt to replace the destroyed one. Anyone know of a good source? What should I look for or consider when buying a replacement bolt.

Regards

RSM

Information

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[Minnesota Joe]

Wow! I hope it's not the ammo -- just ordered a bunch from CMP two weeks ago. Glad your son is alright.

[BrianQ]

It's not the ammo. The likely cause is a burr on the left receiver rail that impedes the smooth rotation of the bolt. It is also possible the bolt was damaged while it was in a different receiver and finally let go.

[frankderrico]

BrianQ, your examples look to be all flat bolts. Is this more common in flat bolts? Thanks....Frank

[American Patrol]

The bolt that came apart on me was a flat bolt as well. It had great original finish and appears(used to appear) almost new.

Regards

RSM

[BrianQ]

The single bolt pictured is a round bolt and it is very close to completely separating.

One of the design changes incorporated into the round bolt was done to make them less susceptible to breaking but they can and still fail in the same spot.

[frankderrico]

Brian thanks,
American Patrol, so glad your son was not hurt. Did you have a round or flat bolt in the rifle?....Frank

[kikokat]

A couple of years ago, I had a NPM flat bolt fail on me. Resulting damage included powder burns on my face (thank God for shooting glasses), a ruined receiver (slide snapped in half and cracked/bent the slide rail), along with splintering a nice hi-wood NPM stock when the piece of slide departed.
Was able to attribute the failure to a cracked R/H locking lug, as shown in Brian Q's photo. Since then, I carefully check the bolt on every carbine I own, buy, or shoot with a bright light and magnifying glass. I've found 2 other cracked bolts in the process.
These things are old, and may well have had heavy usage.
I was fortunate that I and my shooting buddy standing to my right, were not seriously injured.
But I do love these little weapons!

[Steve.]

Its not the ammo, it is the bolt design.

The carbine is really a single lug bolt since the left lug rarely touches anything. This combined with the ability to fire with the single lug only partially rotated into lockup, puts a lot of stress on the single lug that isn't even supported all that well by the bolt raceways. It uses the chambered cartridge by design as the spindle for the bolt to rotate around.

So the flat bolts break sometimes. It is important to check the right locking surface to be sure there is no damage to it that will interfere with a new bolt completely turning into lockup. Likewise, the left lug locking surface is often damaged by the left lug when the right lug breaks off. Check it also for being "smeared" to the rear.

As always, diagnose and repair any carbine that has a habit of failing to go into battery.

[M1Cghost]

Way too tight of head space caused those bolt destructions, thats all there is to it, barrel or bolt change on the receiver without head space guage used!! Plain and simple.

It's not the ammo. The likely cause is a burr on the left receiver rail that impedes the smooth rotation of the bolt. It is also possible the bolt was damaged while it was in a different receiver and finally let go.