Is using shotgun shells loaded with rocksalt a good non lethal home defense weapon?
Anything propelled at high enough velocity can become dangerous. I once watched a demonstration where a candle was fired from a 12-bore shotgun. It had enough force to smash a fist-sized hole in a wooden door. Personally, I’d suggest leaving your shotgun loaded with regular shot, and seeing if you can find a non-lethal alternative which is legal where you live – taser, pepper-spray, etc. If the non-lethal response either doesn’t work – or isn’t appropriate, like when the perpetrator is armed – then go to the gun. Mounting an entry light or laser-sight on the thing to make it more intimidating might also help.