I shoot a lot of 150 grain cast wadcutters over 2.7 grains of Clays shotgun powder. Very mild and accurate. I don't know the velocity but I sure as heck wouldn't want to be shot with one.

I've also shot a bazillion 158 SWC's with charges ranging from the same 2.7 Clays up to 3.0 of Bullseye with never ever having stuck one in a barrel. I've not ever tried a 125 bullet but I can't imagine those same charge weights not working for it too, unless there's a catch with those bullets not being heavy enough to generate enough pressure for efficient powder burn?

"You can lead a man to logic, but you cannot make him think." Joe Harz
"Always certain, often right." Keith McCafferty