I think if you had tested it by shooting some round over a chronograph, you would have discovered that the velocity gained was marginal at best. Simply going to a +P round will NOT substitute for an 1 1/2 inch loss in barrel length.
Depending on the powder used, that 1 1/2 inches could mean a loss of anywhere from 100 to 300fps in velocity. Considering that standard pressure .45ACP usually runs in the neighborhood of 850 (230gr) to 1200fps (165gr) from a 5 inch barrel, that loss in velocity means that your round may not be going fast enough to expand reliably. I feel that it would be wise to test it further and possibly go to a lighter bullet weight.