Something which I have believed for years!
The one I saw involved a fella at the club using an Uberti Colt. Action was getting a bit "sticky" so he squirted a load of WD40 in the mech, via the slot for the hand, in the breech face. Loaded up as per usual, applied whatever mixture to the front of the chambers and had three go off at the same time! His gunsmith told him that the nipples were worn and vapour collected round the rear of the cylinder and igned three chambers with one cap!
As for calibre, I have three .44's and three .36's and I've also owned .45's. I've found my .36's have always been more accurate.