The critical bullet deformation occurs when the factory bullet is pulled from factory .22 cases. The factory roll crimp cuts into the bullet heel and when the bullet is pulled, the heel is reduced in diameter too much to be reloaded. In fact it is necessary to use a case mouth expander to open the factory case mouth crimp to load and crimp fresh cast bullets.
The most amazing thing about shooting BP .22's is the impressive 'Boom' and considerably more fire and smoke than you might imagine. I use a Kirst Konvertor cylinder and barrel sleeve in my .31 '49 Pocket and .36 '62 Pocket Navy with grand results. Being partial to the 'Shooting Strange' concept, I have used the converted pistols and hand loaded .22BP rounds as my main match revolver at monthly Berger matches. Quite a sight to see and hear.