There is no hard and fast definition of a big bore, but we’re pretty safe starting with 40-caliber and clawing up the scale to the 50-caliber. And then throwing in the two novelty rounds, the 600 Nitro Express and 700 Nitro Express. But this doesn’t perfectly define all the big bores, either.
Consider the 44-40 Winchester, the original centerfire big bore. Yes, the .427-inch bullet diameter is what most consider a “big bore,” but at 1,190 fps and 629 f-p of muzzle energy, hardly what most of us expect. The more modern 44 Rem. Mag. revolver cartridge betters that, nudging a 240-gr .430” bullet 1,600 fps for 1,507 f-p. Those numbers aren’t all that impressive, either. Big bores are supposed to be powerful and hard hitting like the famous old 45-70 Govt. Now there’s some bear stopping potential…
Uh, sorta kinda? Our 1873 war horse at factory-loaded pressures spits a 300-gr. flat nose 1,880 fps on a good day. That’s enough to cough up 2,355 f-p muzzle energy. Sound like a sledge hammer? A 180-gr. from a common 30-06 puts out 3,023 f-p. It’s sectional density is appreciably higher than the 300-gr. .458 slug, too. SD of .271 vs. .204.
Why Big Bore Cartridges are Not That Popular — Ron Spomer Outdoors is written by Ron Spomer for www.ronspomeroutdoors.com