Under our laws, the receiver is the firearm. Therefore --
1. Shotgun -- Browning Superposed O/U with matching set of bbls -- 12, 16, 20, 28, and 410.
2. Handgun -- Contender, with a large and varied number of bbls of different calibers, lets say 17 HMR ,204 Ruger, 22LR Match, 22 Hornet ,223 Rem , 7-30 Waters , 30/30 ,375 JDJ, 44 Rem Mag, 45/70 Gov’t , 45 Colt/410 Ga.
3. The Sig Sauer R93 with the bbls/bolt heads for .257 Wby. Mag., 7mm Rem. Mag., .300 Win. Mag., .300 Wby. Mag., .300 Ultra Mag., .338 Win. Mag., .375 H&H Mag., .416 Rem Mag.
4. Rimfire? tough call -- Maybe NEF Sportster with three bbls., 17HMR, 22WMR, and 22LR. Anyone know of a bolt or semi rimfire with switch bbl. capability?
Net result -- 1 shotgun covering 5 gauges., 1 center fire bolt rifle covering 8 calibers, one center fire handgun with 11 calibers, and 1 rimfire with 3 calibers.
OK, I think I am good to go!