I have done more or less the same. A Lee .360 RB ran through a .356 push-through sizer to be shot for plinker loads intended for .380 & 9mm. The goal was to push it hard enough to just cycle the slide on my S&W Bodyguard 380 which is a locked breech gun. With the ball seated will the flat ring created by sizing, seated just below the case mouth and a taper crimp over ball radi. I used a light charge of Titewad and with 45/45/10 tumble lube I ran into leading but powder coated balls shot clean. I did get it to cycle the slide just fine and it feeds th stumpy little rounds without issue.