I don't know that I need another caliber.
I, currently have...
9mm, 45acp, 45colt/454 casual, 7.62x25 in pistols.
.22lr, .223, 5.56, 6.5 Grendel, 6.5 Creedmoor, 7.62x39, 300 blk, 308, 8x57, 450bushmaster in rifles.
A pretty solid stable, if I do say so.