what can't u figure out, hmm?
We CAN match 223 rifle sorts of impacts with a belt pistol, you know. With a 20" barrel, the remaining velocity of a 70 gr Speer Sp 223 handload is about 2400 fps at 100m or so, if it was loaded up real hot. It might well be only 2500 fps at 50m, if the reload was not well-developed and tested. Such 223 hand- loads are well known to work as "well" as do 170 gr 30-30- sp;s, on small deer, feral dogs, etc. That is, not great, but a HELLUVA lot better than do 230 gr .45 jhp's, that's for sure.
A .45 has 4x the frontal area of a 223. For the mathematically challenged, remember "Pi r squared? To calculate the frontal area of a bullet, you have to calculate the area of the circle formed by its diameter. twice the diameter means 4x the area, because the radius is squared, then multiplied x 3.14. ("pi") Frontal area DOES have some saluatory effect at impact, particularly with a prefragmented bullet. So, since the 460 Rowland can handily get 70 grs to 2300 fps in a 4" barrel, these sorts of velocities, (ie, well known 223 sp rifle performance on critters) CAN be had from a belt pistol. An alloy framed, compact, controlable belt pistol, too.