[WWWJD]

Definitely clean from the breech end when you can for the afore mentioned reasons. Nicking the crown is the biggest concern; it's the last surface the bullet touches before leaving the barrel, thus the most likely goof in the barrel to have an effect on accuracy. I have a few that just can't be cleaned this way, namely the Marlin 60. I just gingerly get the jag or brush started and make sure the end of the rod doesn't gouge it. I also use a fiberglass coated cleaning rod.

I guess the best thing I've done recently regarding cleaning is picking up a can of Wipe-Out. Foaming bore cleaner, it dissolves all that crap and makes multiple trips up and down the bore less frequent. There are numerous others that do the same thing, but that's what my local store has and it works.

Don't sweat it too much.