[The_Sword_of_Groo]

I am certianly not advocating anyone do this, as a live shotgun shell is dangerous and should be treated as such. However...
Rock salt, epsom salt, peas, etc all have the same problem. They don't have enough density to retain energy down range. They all will cause damage in close, but are useless at distance. That being said, any one of these loads is effective as a non-lethal method of, say, running dogs out of the trash or something similar. Effective range in my experience is roughly 35 yrds. ( by "effective", I mean stinging a dog's butt without causing any permanent damage) I would limit their use to single or double barrels where cycling the action isnt required.
If you have reached the point where pulling your weapon on a human target is required, use real ammo and aim center mass. Do not shoot to wound.

[The_Sword_of_Groo]

Allow me to make a correction...I should have typed 35 FEET instead of yards. Sorry for the confusion