If I added a caliber, it would likely be one I didn't have to buy magazines for. I buy 15 magazines minimum for each firearm that uses detachable mags. Met a guy who had a drum fed 12g folks drooled over, but only 1 drum...he said when they came up for sale they were $600 used.
12g, all tube mags; .410 (lever action/ tube mag); .357 (revolver - just 2 speed loaders);
Detachable mags:
.22lr, 9mm, 10mm, .45ACP, .300BO, 5.56x45, 7.62x39
I divested of
.380ACP and 7.62x51/.308.
I intend to get a longer range bolt rifle, haven't decided which caliber, leaning to 6.5Creedmoor but .338LaPua, .300WMR, couple others in consideration but I can't even decide on caliber, let alone platform, and it would be highest cost/ least opportunity to shoot, so my budget has gone to suppressors mostly.