If I were you, I'd use 158gr LSWC's. That way the lower velocity won't matter as much, you won't need the speed to expand the hollow point, but you'll still make a nice clean hole. A hot full wadcutter could be used too.
Or if you're forced into even lower velocity go with the old round nosed bullet. That way you'll still penetrate vitals. My target load is a Berry's 158grRN bullet with 3.7gr of Bullseye. It gets 684fps out of my 3" SP101. It's very tame in my 642 and very accurate in both.
Do you have an exposed backstrap? Maybe a full wrap around grip would help too.
anti-state, anti-war, pro-market