Can you fire a .308 round in a rifle manufactured to fire 30-06 cartridges without damaging the gun? - Quora
Could the use of 'adapters' which fit into the chamber and swapping of the bolt, extractor and other parts allow firearms to use different calibers as long as the new cartridge is
Mosin Nagant
223/5.56mm In-Chamber Red Laser Brass Boresight – Firefield.com