Start low with Red Dot
For a hollow-base 148gr. swaged lead wadcutter, I have loaded as low as 2.5 grains of Red Dot and could cycle the action on my S&W 52-2 in warm weather, but I can't recall ever having tried that load in January outdoors. However, I have gotten better accuracy from other powders, notably Trail Boss when I used 3.3 grains, and American Select using 2.8 grains, and there's always the standard load for a flush-seated swaged hollow-base wadcutter of 2.7 or 2.8 grains of Bullseye. 3 grains of HP-38 or WW231 are also very good loads for the 52-2 and here's a tip about a quirk about mine: always got best accuracy with Winchester cases primed with Winchester primers - don't know why mine's like that, but I have test targets to prove it, same bullet & same powder, different primer or different case headstamp, the WW combo beat the others.