357 ammo of any kind won’t chamber in a 350 Legend. Hand loading .357 or .358 bullets in a 350 legend would be real bad.
That could cause a problem.
I gave in and bought a 350 Legend AR15 upper the other day. My primary interest for this one is subsonic loads (with a suppressor), but I'll also be experimenting with full power loads as well. I will be investigating some of the things we're told we "can't" do on this one - using .357" and even .358" bullets, forming brass from 5.56, etc.
It's good to hear confirmation in the OP that the Winchester brass sucks; I had a suspicion of that. Fortunately I found Starline brass for a pretty similar price.
This could prove problematic.