I have shot thousands of 148's with the 2.7 gr Bullseye load.
Factory 148's chronographed 800 fps out of my 4" Colt Police Positive. The 148 LSWC's that I have used did not have extensive grease grooves and pushing them fast will probably cause nasty leading.
These 148's are target bullets and they were not meant to be pushed to +P levels, at least in my opinion.
And older Colts, they were not meant to be used with +P loads. You will batter it out of time with hot loads, and try to find a gunsmith who works on the things.
If I'm not shooting, I'm reloading.