A friend of mine said he had seen some 8 bore shells marked industrial and the guy that had them said they were used in the steel industry for clearing out so the steel would flow. I think they also used a large shell like that to cart start old acft radial engines.
Those are for a Kiln gun used to knock all the strew off the inside of the kilns after they've been allowed to cool. No its not fired from the shoulder, and you don't want to try and shoot any through a regular 8 gauge.
Gun Digest 2010 has an artical on a 2 bore single shot rifle. It shoots a 2500gr to 3500gr lead slug from 1950fps to 1250fps for muzzle energy of over 11,000 foot pounds.