Just an observation from looking / shooting the Martini I have now. If the barrel is 22 rimfire / CB cap, short, long, long rifle; I would believe that the sheer steel mass of the barrel & breech would safely fire any 22 LR cartridge except for the hypervelocity rounds.
Yes, I recognize that heat treating is questionable, non-existent, and unknown. One Half inch of steel will withstand any standard or high (not hyper-) velocity 22 LR rimfire cartridge. Modern cheap, low carbon, low quality steel has a mechanical yield strength = 20, 000 psi. Our Martini rifles can easily handle today's 22 rimfire cartridges less than hypervelocity.
Yes, I recognize that heat treating is questionable, non-existent, and unknown. One Half inch of steel will withstand any standard or high (not hyper-) velocity 22 LR rimfire cartridge. Modern cheap, low carbon, low quality steel has a mechanical yield strength = 20, 000 psi. Our Martini rifles can easily handle today's 22 rimfire cartridges less than hypervelocity.