Don't know where you got data showing a 400 gr cast bullet going 1365 from a 7 1/2" barrel, but having shot several thousand 400 gr cast rounds through a 7 1/2" revolver I'll say 1200 fps +/- is a realistic velocity with 21-22 gr of H-110, and some people are only getting 1100 fps with those loads in revolvers. If you load somewhere around 25 gr of H-110 you might see 1350 fps in a revolver, but I'd wager you'd be running 45,000 psi +.

I know in theory getting rid of the barrel/cylinder gap and adding barrel length should gain you about 400 fps, but from what I've heard the 480 doesn't make tremendous gains in a rifle. So I consider 400 gr @ 1500 fps realistic from the 480 in a lever gun, and that's nothing to sneeze at.

Yes, a 475 linebaugh will feed and fire 480 ammo, basically like running a 44 sp in a 44 mag. But on the flip side if you have a bullet mold designed for a 480 revolver, you can load ammo to the same OAL as a 475 linebaugh and hence have the same powder capacity. Those rounds won't feed through a 480 lever gun.

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275 gr swc, 310 gr lfn, 400 xlfn, 460 wfn. The 460 was too much of a good thing, I think the 400 gr @ 1200 fps is the sweet spot with the 480.