Gallery of Dramas. Broken Enfield Parts!

[jmoore]

Fortunately for y'all, RJW NZ made some good photos of a distressed SMLE Mk.III* fore stock (Post #20), otherwise...

There's no escape, however, as warned- here's a little more:


No.4 Savage rear swivel assembly that's come adrift. Not a major crisis, but probably annoying if it occurred in the field.


Another cocking piece- uncleaned this time, but not as filthy as the others. Failed in "stages" on TWO roughly parallel planes which were joined by the fracture in the center.

Will try for some more shots of this one if anyone's interested.

Have yet to root through the old barrel pile!

[Mk VII]

Seen several of those staked swivels fail. One can get them welded up again, and "good for another sixty years".

[breakeyp]

Fortunately for y'all, RJW NZ made some good photos of a distressed SMLE Mk.III* fore stock (Post #20), otherwise...

There's no escape, however, as warned- here's a little more:

http://i20.photobucket.com/albums/b2...restuff012.jpg
No.4 Savage rear swivel assembly that's come adrift. Not a major crisis, but probably annoying if it occurred in the field.



http://i20.photobucket.com/albums/b2...restuff014.jpg
Another cocking piece- uncleaned this time, but not as filthy as the others. Failed in "stages" on TWO roughly parallel planes which were joined by the fracture in the center.

Will try for some more shots of this one if anyone's interested.

Have yet to root through the old barrel pile!

Playing the Ford Motor Co. game, an FMEA (Failure Mode Effect and Analysis) of the poorly staked swivel could be due to:

For the swivel, material incorrect, material diameter not correct, upset incorrect due to tool wear, out of print or movement of anvil during staking operation.
For swivel base, swivel hole oversize, incorrect material allows hole to deform during staking operation and not grip the upset.
Staking operation: Insufficient pressure during staking, anvil/fixture movement during staking opertion. Slippage during insertion of wire staked area in the base (If that is how they did it).

Without knowing the process, one can speculate even more issues/concerns.

Comment for what they are worth. This speculation would be followed up by a visit to the manufacturer and deep analysis of his assembly process and controls to insure it does not happen again. Apparently Savage didn't get the message or their sub supplier.

[Claven2]

I love this thread, though I can't for the life of me understand those cocking pieces being broken so frequently in that spot. Frankly, apart from resisting spring pressure at the sear, it's not an overly stressed part. The fracture looks, to me, like an impulse fracture and not a ductile one from plastic deformation. This suggests over-hardening in the metal structure, possibly martensitic steel throughout, while Pearlite with a hard surface or Bainite throughout would have been a much better heat treatment goal for these bits. But then, it's possible that the manufacture was bunged up to begin with and the wrong hardness was the result.

The bolt heads aren't failing in tension as the bolt design would not generate enough force on extraction. I'm thinking it's a combination of too much bolt head slop in battery coupled with uneven wear on the locking lugs causing uneven shear stress on firing. Again, the fractures are not from plastic deformation but look immediate.

One failure I've seen fairly often (no pics though) is the receiver wearing out such that the bolt has too much vertical travel causing iffy sear engagement. You see it on receivers with a lot of miles on them, and more often than not a few rebuilds, some of which were probably done in India where one wonders if the armory had gauges.

I have also seen the receiver bridge inserts fall out on some No.4's, presumably from some shock to the receiver.

[breakeyp]

Consider the relationship of the cocking piece and sear engagement. Smartly slamming the bolt home generates a high stress on the nose of the cocking piece as it hits the point of the sear. I suspect that a condition called impact loading might enter here. It has been years since I fiddled with this stuff, but as I remember there were formulas that tried to account for the addional loads encountered when things were slammed together. High loads and the offset difference between the area (notch effect) of the cocking piece body and the extended nose of the cocking piece and the point of contact with the sear nose creats a moment (force moving on a radius of action) that can put quite a tearing force on the cocking piece. If there is a weakness, sharp corner, material hollow/inclusions--- the part breaks. Like many engineering formlas, you have to make real world tests to get the constants you need to make the formula work for that particular case. In school you were given frictional constants for problems but in the real world you had to test to find them and then proceed with the caluclations that may work or may not. Thank God for safety factors where you design for parts to accept 4 or 5 times the expected loads.

I hope this hasn't bored you too much. It is hard to do this stuff without paper and pencill.

[Claven2]

Yes, there is a bending moment about the base of the elongated part of the cocking piece, but the forces involved should be more than manageable for a machined and heat treated part, even a case hardened part I should think. Given the relatively low instance of failure, I'm more thinking there was something intrinsically wrong with the specific parts that broke and not a general design fault at play.

[Brian Dick]

If the bolthead, firing pin, cocking piece assembly isn't fitted and timed together properly, the slapping of the cocking piece on the back of the bolt body will eventually shear it. Myself and others here have advised folks till we were blue in the face that there's a fitting process involved when replacing boltheads. It's not just a case of screwing in a new one and "Bob's your Uncle"! I suspect that many of the cocking piece failures are caused by incorrect fitting of the bolthead.

[Claven2]

I suspect many of the bolt heads shearing off are also due to the same cause. That being said, I find a No.4 bolt head is generally likely to fit right away while a No.1 bolthead requires many spares to achieve a good fit to a given bolt body.

[Peter Laidler]

We've mentioned the rotating action of the cocking piece when it strikes the sear, which also takes a good dollop of impact loading as I call it. But while we used to see loads of broken sears in our Armourers shops, are they a feature in the commercial world as we haven't had a photo of a snapped sear. The young and unwise, the enthusiastic amateurs as I call them, would try to adjust the pull-off by slightly bending the sear. But the sears wouldn't have any of it and snap at the first opportunity.

From the pure engineering point of view, this is a great thread, getting better! I'm inclined to agree with Clav on the broken sears in that it's a failure in the whole of the hardening and tempering process. Put simply, (to take into account my 2nd year metallurgy or hide it!!!!), the sear bents area has to be hard but the remainder has to be tough. I used to see them snap across the safety sear/half cock bent and to see several broken across the 'join' between the two different masses is rare for me but is sooo illustrative.

Breaking across the bolt head tenon/threaded shaft like that is a bit of a teaser and I'm thinking catastrophic due to shock loading (yes, I know you're asking....where does it come from and HOW does it manifest itself there?). That would make a super and interesting student project. Brian has raised a good point and that is the simple fact that the bolt has to be looked at as a whole unit. I wonder if that's why we (in the Military) would see plenty of cocking piece failures across the safety/half cock bent, we didn't see the other failures.

I wonder how the meister Ed H would have interpreted these failures....................

[Son]

We've mentioned the rotating action of the cocking piece when it strikes the sear, which also takes a good dollop of impact loading as I call it. But while we used to see loads of broken sears in our Armourers shops, are they a feature in the commercial world as we haven't had a photo of a snapped sear. The young and unwise, the enthusiastic amateurs as I call them, would try to adjust the pull-off by slightly bending the sear. But the sears wouldn't have any of it and snap at the first opportunity.

From the pure engineering point of view, this is a great thread, getting better! I'm inclined to agree with Clav on the broken sears in that it's a failure in the whole of the hardening and tempering process. Put simply, (to take into account my 2nd year metallurgy or hide it!!!!), the sear bents area has to be hard but the remainder has to be tough. I used to see them snap across the safety sear/half cock bent and to see several broken across the 'join' between the two different masses is rare for me but is sooo illustrative.

Breaking across the bolt head tenon/threaded shaft like that is a bit of a teaser and I'm thinking catastrophic due to shock loading (yes, I know you're asking....where does it come from and HOW does it manifest itself there?). That would make a super and interesting student project. Brian has raised a good point and that is the simple fact that the bolt has to be looked at as a whole unit. I wonder if that's why we (in the Military) would see plenty of cocking piece failures across the safety/half cock bent, we didn't see the other failures.

I wonder how the meister Ed H would have interpreted these failures....................

It seems strange to have to say this (and embarrassing too) but not all sears are as hard as a bulls forehead.

Forgive me Father, for I have sinned...

I was given an sportered MLE (Sparkbrook IIRC) action that needed thirty pounds (measured) on the trigger to release the bent from the sear. The bloke had bedded the action in acraglass about a quarter of an inch thick in sportered No4 foreend without relieving any wood. Then he had cut into the foreend at the front of the trigger guard until the ball and socket MLE trigger and sear reached the cocking piece. The ball and socket joint actually bound tight at full extent of travel before the sear released the bent.

"Can you make it a nice crisp three pounds with minimal drag?" was the request. "Oh, and don't upset the bedding- it shoots ok"

I ended up putting in an SMLE sear and trigger, but the sear was too wide and didn't release the bent. I could have built up the nibs on the trigger, but I thought I'd try something else first. I sat the sear on one end on the bench, the other end directly above it. I then hit it with a hammer! (HARD) Much to my delight it didn't break, but did close up about half a mm and with a little stoning of one trigger "nib" I achieved his "three pounds with minimal drag", assembled it quickly and returned it- resisting the urge to convert the owner to a rifle bucket!

PS, swapped some emails with Mr Horton the other day. He's very good and wishes all his mates here all the best for the season.