No.1 Mk3 Bolt Cracks

[Peter Laidler]

THE ACTION BODY STRETCHING SCENARIO IS A TOTAL MYTH............... I have already put it to bed once on the forum if anyone cares to resurrect the article. Things stretch be being put under tension - as you do with a TENSION spring or putting a bolt under TENSION by tightening it in hole against a nut. I won't go into it again but think about it, whether it's a Bren, L1A1, No1 or 4, the rifle body is always in compression. That's why you get bloody recoil.................. I've got my steel helmet on again, ready to face the wrath of the amateur physicists and metallurgists.

That is where bolts ALWAYS fracture and it is simple metal fatigue* where the bolt is hardened/tempered/toughened across the locking lugs. Looks like an incorrectly fitted bolt or worn body but only metallurgy will show

Calm down dears........
(*not strictly mechanically correct but sufficient for our example)

Information

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[muffett.2008]

I'm sure I've posted pic's of fractures around the small lug before...................that's my excuse to visit the local aircraft maintenance boys and use the crack testing gear.

[Surpmil]

I'm sure I've posted pic's of fractures around the small lug before...................that's my excuse to visit the local aircraft maintenance boys and use the crack testing gear.

As have others here. The granular structure at the breaks in those photos was commented on IIRC. I don't know if that was within the normal range or reflected progressive embrittlement due to stress.

The recoil lug in the body that was in closer contact with the bolt lug would have taken more load than normal obviously. Whether that would cause deformation of the lug in the body I don't know, but are they not surface hardened? Sub-surface deformation? Seems likely that the lugs would already have already "compressed" from prior loading as much as they ever would?

As for bolt "set-back" during proofing I will leave that to the experts to explain as well!

Another virtue of the design seems to be that if the bearing is unequal the worst that can happen is this kind of failure, rather than ejection of the bolt, because no matter what happens, that large recoil lug isn't coming off the bolt body.

[RobD]

Peter, have I understood you correctly?
Do you say that
(a) the Lee Enfield action body never stretches [or at least, never stretches significantly];
and
(b) this is because the forces produced on firing compress rather than stretch the Lee Enfield action?
Rob

[Pzkw38]

Yes, that does not make sense, the bolt will be compressed by the charge, react on the action which will be in tension from the bolt engagement to the breech. Else that bolt is moving rearwards.

[Homer]

Peter did you see this type of failure often in service?

[mrclark303]

Interesting, never seen a bolt body crack across before, only cracked and fractured action bodies.

Was this more an SMLE thing than a No4 Peter?

[mrclark303]

So not stretching (getting ready to put on the dunce cap here and face the wall)

Compression damage to the action body from bolt failure, would that be right Peter?

[Peter Laidler]

Did I see the failure often in service. No. Once on a bolt taken from a rifle in the 80's. oince on a civvy rifle that Fultons had in their collection and another on a sample bolt set up tio fail by students that was analysed as catastrophic metal fatigue loading. I wouldn't say that it was a No1, 4 or 5 failure. Just a failure across the hardened/toughening part of the bolt - just something to look out for every now and then. The steel won't give you any notice (JMoore ?) there, it'll just go but the bolt will not cause you injury when it does. It won't happen again because you won't be able to re-load!

Good Q Clarkie. But no compression damage to the body because the shock loading of discharge has already passed through the body and on to your shoulder in the form of recoil - and that loading was via the locking shoulders in any case. As I said, there won't be a next shot with that bolt!

Maybe someone wot is compu'a savvy can bring up the article wot I writt about 'stretching' bodies some time ago.

[David TS]

Peter

Was this it?

Was it a post in a thread, or a thread title?

http://www.milsurps.com/showthread.php?t=51064