Cracked Right Lug........

[DaveHH]

Nice wood too.

I'd sure check that left side rail on your NPM. BQ says that most all bolt failures are caused by problems with that left side slot. You could just change it out and have the same thing happen again. I have some of the LC 72 or 74 that CMP was recently selling. I normally use my reloads too, but the LC stuff sure didn't seem to be very hot at all. Feeds and runs the gun well, but not some HV stuff.
I guess we should expect failures in 70 year old weapons made in a big time rush. The bolts, f.p, and extractors were the most troublesome parts, mostly because of poor heat treatment.
D

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[painter777]

Sounds like I'll have the house (plus pets) to myself Tuesday.
I'll tear into it then and pass along anything I find.
Too many irons in the fire to be able to concentrate on it today.

Wanted to mention (since mentioning pets) I've been listening to the Milsurps radio while on.
My Daughters: " Left home for the parents Love bird " goes nuts when it hears some of the old military tunes.... Especially Fife and drum. I should U tube it.

Cheers,
Charlie-Painter777

[topaz]

Attachment 48047 Very nice painter

[painter777]

Very nice topaz!
That's the only kind of 'Crowd' I am comfortable in.
1 or a 100 they are just so warm and cozy... Ha!
Now if that were a people crowd of say 1 million, I can guarantee the weirdest SOB in the bunch will come find me. Someone about like that sign language guy down in South Africa

I took a couple pictures of that cracked NPM Bolt before I tear it out.
Standing in the shade of the covered roof at my local range, like I stated earlier it looked like a scratch or piece of rag fuzz. After stepping out in the sun shine and running my fingernail over it... I knew it was trouble.
Started trying to remember it's last shooting session and seem to recall a different metallic sound as I finished up, but can't be positive if it broke/cracked on the last couple shots or a few mags before the last serenade. I do recall finishing up firing it as hard as it would cycle.

If anyone is interested I'll take more pics after I take it down.

Charlie-Painter777

[kosmolinekid]

Good wake up call for me I totally forgot about Flat Bolt lugs . I think that's why the Round Bolt came about right ? Funny about 3 months ago I replaced a Winchester Round Bolt for a Flat one . Everything on my Winchester was early War except the Bolt and the Rear Sight . The Bolt was a no brainer but replacing a Rear Sight is something I won't do .

[painter777]

Kosmo,
You might want to read this:
Weekend Inland Mishap

Pulled the Bolt. I can see the crack carries on toward the back of the right lug, down to the hole for the Extractors stem.
Carbine is pretty greasy.... but don't see any chamber damage at this time.
I'll clean up the Receiver and look/feel closely for any burrs on either inner rail.

Charlie-Painter777

[DaveHH]

Wow! That thing is ready for a catastrophic failure.

[imarangemaster]

IIRC, the pressure is absorbed by the right lug, with the left lug having a back-up function.

[Bubba-7]

DaveHH,
" BQ says that most all bolt failures are caused by problems with that left side slot. " I believe he posted something like this on CMP a while back.
I do not see how that can be true. The left lug does not take any load. It is a safety catch if the right lug breaks. If you check the drawings and add up the tolerances, the left lug is to be 0.001" +0.003" farther back than the right lug. The location of the right lug is 1.191" +.002".
Also a GI test bolt only has a right lug. I am sure if you had a receiver that was perfect on the minimum side and the left lug took some load, that would really help the bolt. But designed to do that does not seem to be the case.

[DaveHH]

Hi Bub,
I believe that his information is about how a rough left rail can inhibit full closing. It could also be that a beat up left lug can be in contact and move the load bearing right lug away from contact with its recess which would in fact bust it eventually. I believe what he says since he knows about a zillion more things about carbines than I do. I'll leave it to him to explain.