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
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7.62x25 Rifle Chamber Insert - 180308, Gunsmithing at Sportsman's Guide
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12GA to 22 Magnum Shotgun Adapter - Chamber Reducer - Stainless Steel
improvised 30-30 to 7.62x54r chamber adapter FAIL - YouTube
TFB Review: The Shooters Box 577/450 Chamber AdapterThe Firearm Blog
7.62x54R to .32 cal. Multi - chamber Insert - 167404, Gunsmithing at Sportsman's Guide