I've used a hammer on a very small scale. Of course the real trick is to breakup the salt without breaking open the bag. Might try laying a block of wood on the bag and hit the wood with the hammer. :dunno:
Dropping on the ground does nothing .... I opened up like 10 bags today and threw them in an old watering trough I had and went to town with a digging bar , broke up fairly easy ... now I need to get my 5 gallon buckets out for when I need it.