Congratulations on purchasing a nice little 20 guage. That is a great gun for a youngster or a lighter gun for you to carry. 20 guage will kill anything a 12 gauge will, it just is nicer to carry and doesn't bark and bite quite as bad on the shooter's end. I am not an H & R expert, but I have looked at them some so I can answer some of your questions. The barrel is stamped "mod" because it has a fixed modified choke, not a screw in choke. Actually, modified is my favorite choke for most hunting applications. You can't shoot ducks a mile away and its too tight for really close in fast action, but for most general purpose hunting it works fine. You can shoot slugs through a modified choke barrel. Don't buy the high priced saboted slugs. Buy the cheap $5 a box Remington, Winchesters, or Federals. You'll have to shoot it to see which it likes best. You should be fine to 50 yards, probably fine to 75 yards, and 100 yards is about the maximum you could ever hope for. You've only got a shotgun bead on the end of the barrel so you have to play with it and figure out how to hold. I know that sounds really primitive to you guys from center fire rifle states, but Iowa is a shotgun with slug or muzzleloader deer hunting state and you can't believe how many guys hunt deer with their smooth bore shotgun and slugs. Figure out your effective range and don't try shooting farther than that and you'll do fine. I don't know the H & R specifics so I'll let somebody else help you with those questions. Enjoy.