Ok I got it. I had a round that didnt get powder, so when the primer went off the bullet moved forward just enough to keep the cylinder from rotating. A dowl rod and some light hammer tapping pushed the bullet back down and I was able to free it up.
I was worried there for a moment, I just bought this SP101 used and thought I had some serious problems. So for now the dowl and hammer stay in my range bag and obviously only factory loads when carrying.
And, yeah, be extra careful with the handloading.
I've stopped loading .38 on my Pro 1000, because the angles on it are such that it is difficult to reliably visually check that powder is in each case.
"As was the man of dust, so also are those who are of the dust, and as is the man of heaven, so also are those who are of heaven. Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven. "