my friend loads some kind of 255 gr.bullet for his 45.they are accurate and fast out of his 7 1/2 rbh.i recently bought a 4 5/8 rbh.we shot last week and my 45 with the short barrel was more accurate than it should be!he also loads a mean 340 gr.cast load that puts you back a step.the june 2003 issue of guns&ammo has "hot"loads for the 45 lc.they have a 300 gr.bullet doing 1,200 fps.then a 350 gr.going 1,100fps.so yes the 255 gr. should do what you are looking to do.do the bullets have gas checks on them?with the speed you are after a bullet with a gas check should work better.good luck with this overlooked and underloaded,powerhouse! jim257