I was thinking....and then I asked myself, "Why is .30 cal so common in firearms today?
There are so many cartridges chambered for .30 (give or take)
For example: .30-30, .30-06, .300 Win Mag, .300 Wtby, 7.62x51 NATO, 7.62x39, 7.62x54R, 7.62x25, .30 Carbine, .300 H&H, .300 Savage, .30-40...