Ed's right- it's possible - I've seen it myself - very bad burns on the fellows hand.

I've never heard of it happening with a heavy denim patch that is properly lubed and used along with a ball that is only .005" smaller than the bore.

If you shoot any sort of wads or limp-wristed ball/patch combinations, they perhaps you should swab between shots.

If you shoot, for instance, a .445" ball in a.45 rifle, with a.022" denim patch "properly lubricated", you will never have an ember left in the bore.

As longknife said - NEVER pour powder directly into a bore from a flask or horn - that's just plain stupid and asking for a freak accident. Anyone who does that is probably on a 'short list' to the ever-after. The Lord give us choices - you can choose that short list - or not - it's up to you. Just because some buffalo runners loaded that way does not make it OK for you. They also spit balls into the muzzle from their mouth-full of balls. I wouldn't advise that one either - the carrying nor the delivery system. Lots of those guys died becasue of their stupidity.