If not a 44 or 45 Colt with 300 gr bullets-then an 1886 or pre-war Model 71 in 450 Alaskan.
The 1920s half-magazine 1886 in 45-70 -nickle steel-will push a Kodiak 400 gr FP
up to 1850-1900 FPS.The extra lightweight Winchester 1886 does'nt weigh but about 6.75 pounds.
Faster than a bolt action for repeat shots. Might be
