For what it's worth, I have heard that it had something to do with incomplete chamber support, but years ago I put quite a few of my handloads with cast bullets through my 9mm Glock.
I was shooting regularly, almost daily, on an indoor range and periodically I would swipe the bore with a tornado brush. These were pretty light loads with plain base bullets, not gas checked and worked just fine for practice. Didn't try it with higher pressure loadings.