Nabs, your beautiful Mauser stock is self-destructing.
The CAUSE of the problem is that the wood is a century old and has dried out thoroughly. This robs it of strength and resiliency.
I have dealt with this problem a number of times over the last few years, so here's what I do.
FIRST, get a kit of Acra-Glas LIQUID.
SECOND, go to the vet or to the drugstore and get a hypodermic syringe, 5cc or larger, 10 or 15 preferred. Might cost a buck.
THIRD, head for the auto-parts dealer and get a can of Brake-Kleen.
FOURTH, set yourself up with a Crescent Wrench (about 12 inches or 18 inches) and either a variety of wide screwdrivers and wood chisels OR a selection of steel bar-stock in widths from a half-inch to an inch and a half.
FIFTH, lay in half a dozen 3-inch C-clamps and half a dozen cheap washcloths.
Take the stock outside and flush it completely with the Brake-Kleen. This should remove any and all oil near the surface of the wood and leave you with a dry working surface. Be sure to squirt a bunch down into those cracks. You use the Crescent Wrench and the screwdrivers/chisels or whatever to wedge those cracks open while you do this.
Let the stock STAND an hour after doing this.
Now, pad the butt carefully, put it into your vise and clamp it in solid.
Mix up about half an ounce (15cc) of the Acra-Glas Liquid and suck it up into your syringe. You don't need the needle, so trash that: use just the syringe itself.
Now, with your Crescent Wrench and wedges, being careful not to twist hard enough to damage the wood, wedge open each of those cracks in turn, squirt it full of Acra-Glas and let it return to normal.
When ALL of the cracks have had their dose of Acra-Glas Liquid, get out your washcloths and your C-clamps and start padding the stock outside of the cracks, then clamp each washcloth solid. Be sure that you don't clamp TOO tight: you do not want to mar that beautiful old stock.
Now you can trash the syringe; anything remaining in it will set up as solid as rock and there is just about zero chance of re-using it.
When you are finished, let the stock STAND for 12 hours, THEN take a paper-knife or Exacto-knife or something similar and TRIM off any excess Acra-Glas which has worked its way out of the cracks, trimming FLUSH with the wood. Once this has been done, you have a stock which will NOT break again in those places.
The remaining PROBLEM is that the stock now is even drier than it was before you started and thus even MORE prone to cracking. Get out your Raw Linseed Oil and give the INSIDE of the woodwork a nice drink of oil. If it dries out immediately, give it another drink. When the oil starts to remain on the surface, THEN you wipe it dry, let it stand overnight and then give it a final coat of DOUBLE-BOILED LINSEED OIL to seal everything in. Let her stand for 3 days, then reassemble your rifle.
Your problem should be CURED and ought not return for another 25 years or so, if even then.
Sorry that this is a week-long job, but that's how to do it right. You can take some solace in that it took 90 years for the problem to surface; a week is okay for solving it!
Hope this helps.
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