What caused this crack?

[TheGreenMan]

I think this may be the best place to post this. If not please put it in the correct area.

There is a discussion going on at a firearms forum I visit about what caused a crack in a 1942 German WWII rifle. There has been some debate about it being a stress crack from the heat treating, a crack cause by too much pressure from an overloaded cartridge causing the bolt to be set back and putting undue stress on the receiver bridge, from the receiver hitting something/being twisted or a combination of the above.

I was wondering if any of you could shed some light on this interesting little puzzle. The thread is located here. If you can not see the pics without signing up I will see if I can post a few here.

Edited November 29, 2009 by TheGreenMan
added pics

[Rob Browne]

They want a log in :(

[David Einhorn]

I have more questions than answers:
- Was the rifle made at the beginning of the war, or near the end of the war, possibly by slave-labor? I have a vague memory of someone saying that some brave souls who were working as slave labor would sabotage guns that they were making.
- What is the track record of this model? Is there a known problem with a batch made at that factory?

[jimbob]

must have taken some kind of direct hit. as of the dozen or so custom Mausers I've made that bridge is really soft I contour them with a file...did the crack just now show up or was it after shooting the rifle. thats right at the third locking lug ...what do the other locking lug look like any set back ?

Edited November 29, 2009 by jimbob

[ArtWerkz]

I am with Unicorn, also perhaps to hot a load.

[Bentiron1946]

I think it was a bad job of heat treating and most likely a hotter than normal load. When I was building custom rifles up with Mauser actions I tended to shy away from late war actions. Some, not all, were rather brittle like old Krag bolts and actions.

[bnewberry]

Is that the only crack? The reason I ask is that it appears to be at the rear bridge. This part of the action isn't subjected to nearly as much stress as the front bridge because the front of the action (where the barrel screws in) is where the bolt lugs engage locking lugs in the action itself.

I'd say that the action was improperly tempered, left too hard, and subjected to stress of some sort, but not necessarily an over-pressure round.

[TheGreenMan]

I'm off on a job so I'm not near my computer much so I don't have as much time to visit as I normally do.

If you go to the link you should be able to at least read the posts there. They give a lot more info than I have and go into some greater discussion as to the cause than I did.

This is the only crack in the receiver. There is no indication that the receiver was hit or torqued by anything (meaning no dents or scratches of any significant size). The headspace has not been checked to see if there was any small set back to the bolt. There was no easily noticeable set back and the bolt still travels freely in its raceways.

[SGropp]

I've read that towards the end of the war, the Germans were adding sulfur to their steel to speed up the machining of armaments. This had catastrophic consequences when they invaded Russia . They had terrible problems with equipment cracking in the extreme cold of the Russian front.

[Kenzie]

The fracture appears to be fatigue failure