Question on Oberndolf Action

[Pirate69]

I have a Model 98 action that I am trying to debarrel. It is marked as follows"

1920
WAFFENFABRIK
OBERNDOLF
1910

It appears to be a Large Ring Action. But I think I remember reading somewhere that these actions were Large Ring diameter but the threads were smal ring diameter. Am I remembering something wrong? It has a band on the barrel that butts up to action. I assume that it is just soldered on? The barrel is in so tight that I am having trouble getting anything to hold the barrel without turning. I good action wrench is not a lot of good if you can't hold the barrel. Still working, slowly, on it.

Information

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[Patrick Chadwick]

It is, of course OBERNDORF not OBERNDOLF.
Sounds like a Gew98 from 1910 that was taken over by the Reichswehr (hence the 1920 stamp added above). Standard Gew.98 /Kar.98 action had large ring and 1.00" OD 12 tpi Whitworth form threads (i.e with 55 degree incuded angle). Yes, you read that correctly - Whitworth threads!

So an American 60 degree thread would theoretically only make a line contact near the top of the thread. Since large number of 60 degree threaded barrels have been fitted to Mauser actions over the decades, and I have never heard of one coming loose, I imagine that, when properly torqued, the distortion of the thread crest provides secure engagement.

I assume that it is just soldered on?

No other way in those days. You need a hot air blower or very carefully applied gas flame to warm up the entire region of the barrel for some time and then a more concentrated heat to melt the solder joint. No soldering iron that I know of will put enough heat into the barrel fast enough, and the solder must melt all around the ring at the same time. And even when the solder melts you will have to wiggle the ring pretty firmly to shift it. It will probably have been a push fit when new, so do not expect it to fall off!

Then you can go for a walk while the barrel cools down - you have a large piece of very hot steel, and it is best to let it cool down naturally.

The barrel is in so tight that I am having trouble getting anything to hold the barrel without turning.

You need a co-worker to heat up the action ring to a "soft solder" temperature while you (try to)turn the barrel. But do not overheat either the barrel or the ring. Empirically, use the same amount of heat that you needed to unsolder the handguard ring.

[Pirate69]

Thanks Patrick.

"Since large number of 60 degree threaded barrels have been fitted to Mauser actions over the decades, and I have never heard of one coming loose, I imagine that, when properly torqued, the distortion of the thread crest provides secure engagement."

If I understnad you correctly, even though the threads may different somewhat, it may still be possible to use a commercial barrel threaded for a K98?

[Patrick Chadwick]

I understnad you correctly, even though the threads may different somewhat, it may still be possible to use a commercial barrel threaded for a K98?

Well so many seem to have been done, that it obviously works. Presumably a competent barrel maker can make a slight adjustment in diameter to compensate for a 60 degree sharp thread being screwed into a 55 degree thread with a rounded crest (Whitworth).

[Calif-Steve]

Original 1910 barrel? Likely rusted on hard. Try 2-3 drops of Kroil into the receiver and stand the barrel on the muzzle. Keep the Kroil going for 3-4 days. That barrel will come off, good luck.

[Patrick Chadwick]

I just telephoned Lothar Walther - the German barrel-maker. They use the correct 55 degree thread form for their Mauser barrels. To use a 60 degree form would seem sloppy to me. Since even I have Whitworth form tools in my cellar workshop, I see no reason for a commercial manufacturer to cut corners in a way that seems to me to pose a safety limitation.

For those misguided souls who like to have "hot loads" for their milsurps - just consider this: The low area of contact on the thread faces between a 60 degree male thread (barrel) and a 55 degree female thread (action) means that if the pressure is high enough to expand the chamber, the action ring will not provide much support until the threads have distorted so much that they are fairly fully mated, at which stage, the chamber is probably past its elastic limit - i.e. in the process of bursting. In other words - you are relying on the barrel strength alone.

If my thinking is erroneous, I would welcome an explanation in engineering terms (not anecdotes, please!).

[jmoore]

Probably not worth getting all technical. Because if you are at that sort of pressure level, failure at other points have likely already started. Let's just say the threads don't matter much in this situation.