yes i have done it
Unless specifically prohibited by the owner's manual, yes
Yes
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Can't be answered without knowing what it is choked.
As long as the slug barrel is smooth bored(does not have rifling) then it can be used with bird shot.
Firing lead shot through a slug barrel will not damage the barrel. The rifling will distort the shot pattern and you will get less than desireable results.
Yes, I have actually done this myself. I was out hunting with my cousin and I thought he was a deer. My instincts kicked in and I shot a slug straight at him. Luckily, I'm a very poor shot and I hit his model 1000 instead of him, but let me tell you, the slug went right through the gun and kept on going. So yes, it is very easy to shoot a slug through a 12 gauge model 1000 Smith and Wesson pump shotgun, as that's the exact model my cousin Darrell had been using. I don't know why you'd want to do this, but I guess you can do whatever you want with your guns.
That is correct.
Yes
yes
to test it take apart a 410 slug and see if it fits through
It shoots a slug instead of shot.