I've only recently tried them myself, but my friends have been cloth patching 14 bore round balls for their full choked 12 bore duck guns for the past 20something years, without trouble. Due to the necessary fibre wad beneath the patched ball, the patch cannot stay in the bore any more than a wad could. Even if the patch pushed back off the ball, the following wad, which is pressing already on the patch's base, along with the ball's bottom, will shove it out the bore. That wad beneath gaurantees the patch comes out. The accuracy I've (and my friends) have achieved with them shows they always perform as they should.

Where to get a crimper? Making one would be the easiest, I suppose now that I think about it. It is used with a shotshell press like my old Herters, the Mec's, etc, or with a hammer. Due to the fibre cushion wads, the ball can be pushed down flush with the top of the case, allowing the case to crimp properly, then it springs back up against the crimp, which holds it in the case.