You can shoot both 2.75" and 3" shells (just not 3.5" magnums). The "MOD" is short for Modified, which is right in the middle of the choke scale (full, improved modified, modified, improved cylinder, cylinder (none)). Yes, you can shoot slugs through it - buy rifled slugs so they spin for better in-flight stability, because your barrel is not rifled like a dedicated slug barrel would be. 00 Buck is fine.
I don't shoot because I like guns, I shoot because I hate paper.
There's a mistaken impression that conservatives don't like the environment. We do, we love the environment. We just call it the outdoors and we go there to kill stuff.