I have a .455 that has been converted to .45 acp. I shoot only mild
hand loads with cast bullets in AR brass, no .45 acp jacketed bullet
loads. However, I think that the over size chamber throats of the .455
will serve to keep chamber pressures down reletive to the .45 acp in
revolvers originally made for the acp. This is evident in the lower
velocities seen with the same loads in converted .455 revolvers than
seen in revolvers originally made for .45 acp.