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
Miniature calibre (caliber) adapters and conversions
The Utility of 12-Gauge Caliber Adapters, The Good, Bad, & Ugly -The Firearm Blog
iunio Universal Gun Cleaning Kit, with Mat and Case, Full Brass Jags, Rods and Adapters, for All Guns, Rifle, Shotgun, Handgun, Pistol, Hunting, Shooting, All Caliber
X-CALIBER Survival-Rifle Gauge Adapter System - Soldier Systems Daily
Shoot any round through any firearm with subcaliber adapters - Carolina Sportsman