Get, among other things, a chamber cast and an accurate measurement of the headspace done.
The chamber cast will tell you how oversize the chamber really is. As was touched upon earlier, the military was not at all concerned with how much the case stretched, as long as it worked once per case, so the difference in size between a minimum size case, and a maximum size chamber, is, well, huge. Worth digging out the SAMMI (SAAMMI, SAAMI?) drawings of the cartridge and chamber for the caliber, then realize that as loose as that is, the military chamber was looser! There are several old chamberings that suffer this problem. .22 Hornet comes immediately to mind.
Like as not the easy fix is to have the smith pull the barrel and take one or maybe two full turns off the face of the shoulder and the breech, then recut the chamber, with an eye towards a little closer tolerance. Ideally, with a reamer that is much closer to 'modern' tolerances WRT maximum cartridge, minimum chamber sizes. A look at the size of the cartridges coming out of the sizing die would be in order too, I think.
This will cost a bit, but so will any other solution other than hanging the rifle up and retiring it.
The rubber spacers, along with some careful neck-only sizing, should help with the case life a bit.
If you full length size, this adds to the problem as it is working the brass back and forth and allowing it to stretch a lot more each firing.
Good luck!
Cheers
Trev
