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Shooting & Reloading - Mausers, Big Bores and others >> Mauser Forum Photos & Archive

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mehulkamdar
.416 member

Reged: 09/01/04
Posts: 3688
Loc: State of Ill-Annoy USA.

Zimhunter's Custom Siamese Mauser
#141132 - 25/08/09 09:00 PM

I have two pictures of Zimhunter's beautiful custom Siamese Mauser full stock carbine. He tells me, "I'm very pleased with this little carbine in both looks and performance. Bought it from a friends gunshop and he was reluctant to tell me who built it and I never pushed the point. It was not fully finished not having a safety and was not checkered. I put an FN style safety on and a friend Sterling Davenport graciously put a couple of panels on it." The little rifle is chambered for the 30-40 Krag.

Hope you enjoy the pictures, and if you have any questions, Zimhunter should be here shortly.

Good hunting, everyone!

--------------------
The Ark was made by amateurs. Experts built the Titanic.

Mehul Kamdar

Edited by CptCurl (19/10/09 12:43 AM)

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rigbymauser
.400 member

Reged: 15/05/05
Posts: 1972
Loc: Denmark

Re: Zimhunter's Custom Siamese Mauser [Re: mehulkamdar]
#141161 - 26/08/09 05:41 AM

Dandy little rifle indeed...and ofcouse, kept it in a rimmed caliber. Thumbs up for the project

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Zimhunter's Custom Siamese Mauser [Re: rigbymauser]
#141371 - 31/08/09 03:43 AM

Please take note of an experience that I had:

A few years ago I built a sporter for myself using a Siamese action, .45-70 caliber. I kept it for a while and sold it on Gunbroker. As I was prepping the rifle for shipment, I checked the chamber and closed the bolt - firmly, but not violently. To my shock and dismay, the cocking piece popped off and landed in my hand! Since the bolt was closed, and the striker (firing pin) was fully forward, the bolt was locked and couldn't be opened. Upon some consideration, I passed a dowel down the bore and depressed the nose of the striker enough to allow the bolt to be opened.

Upon examination, I saw that the failure originated at the root of the last lug of the striker, where the cocking piece ended: this is the area of maximum bending moment, and the area most likely to fail. The inside corners of the lugs were made with minimal radii, i.e., they had very sharp corners, ideal stress risers. The failure appeared to be a brittle fracture with little evidence of ductility. Fatigue did not appear to be a contributing factor.

I quickly obtained a spare striker from Numrich and was able to send the rifle on its merry way. Before it went out, however, I ground and polished a generous radius in the roots of the lugs to alleviate stress-risers. During research, I found that early Mausers had sharp corners but later ones were generously radiused. Maybe this had happened before?

If I had been shooting the rifle, the falling striker would have probably ignited the cartridge while the bolt unlocked. That would have likely spoiled my morning; it would have been worse had it happened to the new owner. I don't know with certainty that all Siamese actions suffer from this fault, but one would be wise to check.

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zimhunter
.333 member

Reged: 05/02/04
Posts: 388
Loc: Southern Arizona

Re: Zimhunter's Custom Siamese Mauser [Re: Carpetsahib]
#141385 - 31/08/09 01:35 PM

Carpetsahib,
Thanks for the heads-up but I'm not quite sure I understand exactly what you are saying happened. I don't fully understand WHAT broke off WHERE and how did it lock the bolt from opening. I don't understand what you mean by 'bending moment' as the striker/firing pin works either forward or rearward or axially and never bends. At the moment of firing the firing pin is in it's most forward position and does not in any way lock the bolt that I can see.

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Zimhunter's Custom Siamese Mauser [Re: zimhunter]
#141401 - 01/09/09 12:57 AM

Sorry about my use of engineering terms and the resulting confusion. If you disassemble a Mauser bolt, you will find that the Cocking Piece (which engages the sear on the trigger assembly) is attached to the Striker (firing pin) by means of a series of Lugs (the Lugs are machined on to the rear of the Striker, six in all). The Lug that is closest to the middle of the Striker lies at the inward edge of the Cocking Piece. When the Striker/Cocking Piece assembly is under load from the Main Spring, as when the rifle is prepared to fire, there is upward pressure exerted on the Striker Assembly (resulting in a Bending Moment*): the maximum stress is found at the point where the Striker Assembly is least supported, i.e., where the end of the Cocking Piece lies. And that was the exact spot where my failure occurred.

If you will further examine a Mauser bolt assembly, you will find that the Striker has a flat section immediately behind the actual firing pin portion: that constitutes a lug that engages a machined area in the interior of the bolt when the striker is fully extended. This engagement prevents the bolt from rotating when the striker is fully forward. Just pressing the nose of the Striker (firing pin) back level with the Bolt Face is enough to unlock the bolt.

* Just Google "Bending Moment" for an explanation of this term.

Hope this clarifies the situation somewhat.

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zimhunter
.333 member

Reged: 05/02/04
Posts: 388
Loc: Southern Arizona

Re: Zimhunter's Custom Siamese Mauser [Re: Carpetsahib]
#141432 - 01/09/09 03:25 PM

Thank you very much for your detailed explanation. I'm sure I'm just dense but I really don't see what is causing the 'upward pressure' on the striker. The firing pin spring goes around the pin and just applies pressure straight forward. When the rifle is fired this moves the striker forward to impact the primer so why does the bolt not lock everytime you fire. I'm obviously missing something but thank you very much for your concern.

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Zimhunter's Custom Siamese Mauser [Re: zimhunter]
#141443 - 01/09/09 11:18 PM

It is hard to describe what would become clear with an illustration. True, the spring pressure is more or less linear. The Bending Moment comes from the fact that the Sear/Cocking Piece interaction is off-axis, thus establishing parallel, but off-axis forces. These parallel forces constitute a Bending Moment.

Concerning the bolt being locked by the Striker: it is locked each time the rifle is fired. You don't realize it because the Striker is cammed back by the bolt when the bolt handle is lifted. If the cam surface is missing (as when the Cocking Piece breaks off), the Striker cannot be retracted. Ergo, the bolt is locked.

Now early Mausers didn't have this feature and I suppose this may be true of some Siamese rifles.

Hope this helps.

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