Kar98k - Reciever, Surface hardened or thru-hardened? (WW2-Style LSR project)

As some may remember ( and probably don't) I was starting a Kar98k WW2-Style Repro LSR Scope project. I got my scope, have a nice BNZ russian capture to put it on, but discovered that the receiver is hardened in some way or another.

If the reciever is surface-hardened, it should still have the capability of being tapped for a LSR mount. (With some effort)

If it is thru-hardened, it may not be possible to tap the receiver for the mount.

Anyone had any experience drilling this receivers for a LSR mount? Anyone know how the receiver was hardened in WW2?

Thanks!

The WWI Mausers were surfaced hardened. However, just prior to the start of WWII the Germans developed a new technique. They hardened the receiver through and through. As they used a very plain steel, it was a real breakthrough. Good luck with the project.

Thanks Steve. I may have to find an alternative method, maybe threaded inserts.

Perhaps carbide taps help?

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Originally Posted by Calif-Steve

Perhaps carbide taps help?

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I was thinking of that today, I'm going to ask a machine shop I used to work for if they have any ideas.

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Originally Posted by Calif-Steve

The WWI Mausers were surfaced hardened. However, just prior to the start of WWII the Germans developed a new technique. They hardened the receiver through and through. As they used a very plain steel, it was a real breakthrough. Good luck with the project.

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Far as I know and have read, all Mausers are low carbon steel case hardened. To be hardened "through and through" would require at least a medium carbon steel instead of a low carbon steel. As a result of hardening "through and through" you'd end up with a brittle receiver. Where did you hear this?

Dutch

The suface hardness ( case hardening ) is what makes them strong but very slick to operate. As far as I know no Mausers were ever made hardened throughout, there would be no point.

I read a very extensive article some years ago. I think I saved it. In WWI the Germansd used a paste and surfaced hardened their Mausers. It worked quite well. However, just before the start of WWII they developed a new technique to harden their receivers. They used that system in all arsenals. It was a through and through treatment. I think the common heat treatment of today is a form of that technique. WWII Mausers tend to be very hard, but not brittle. They must have figured it out. I did find this:

From "Hartevorschriften" booklet (hardening instructions) dated Sept.26, 1933, found within the Mauser Oberndorf archival notes after the war.

"Durferrit" refers to a proprietary dip, full name "Durferrit-Zyan-Hartfluss" which replaced the usual cyanide dips of the era. The only elaboration on this is: "....due to certain additions in the Durferrit over the common dip, the melting point of the dip is much higher; pieces would reach hardening depths up to .7mm within one hour. Besides the time saving advantage, parts were fully hardened over their entire surface".

Receiver: Place in Durferrit bath for 15 min at 850c, then air cool. Heat rear of receiver well and head of receiver one after the other in Durferrit bath to 770c, protecting receiver middle, plunge in oil and relax in oil bath at 180c for 30 min. Strength- shell-file hard at the receiver head (20 degree) 23/28 degree R. Change: Addition: Temper in salt bath for 5 min at 500cI did find this:

Interesting stuff, Steve. The .7mm hardening depth is around .030 inches which is considerably deeper than any surface heat treatment I've used. Usually cyanide dips will penetrate around .005 in. with one dip and can go deeper with repeated dips but I've never gotten anything close to .030 in. Still not hardened throughout by any means. When fully hardening larger pieces uneven heating can be an issue(e.g., small areas being overheated while larger diameters are not hot enough) for quality control.
For drilling and tapping Mauser actions I would think a carbide endmill or drill could be used to poke a hole through the hard skin and then drill and tap with HSS tools.

I am trying to recall an article. I thought the article discussed very deep hardening. But, this is from memory. I thought the Germans liked this method, as they basically could double the hardness of the steel. But, this technique does not penetrate through and through.