There are two types of slug barrels one is rifled and one is what they call a smooth bore, when I was a kid there was only smooth bore (without rifleing) and these guns shot the standard 1 oz. lead slug and were good for around 70 yards, 85 yards was a hail marry, today with rifled barrels you can shoot higher quality ammo much greater distances twice as far as the old school stuff, I will say this I have a youth modle 870 express magnum in 20 gauge that is a smooth bore that will print all over a paper plate at 100 yards pretty good for old school, I use it to this day casue it is so little and light it is a pleasure to hunt with, as far as letting loose of both barrels at the same time, those were really old guns that you were able to do that with, they used much less powerful rounds I think they were 2 inch or 2 1/2 cant remember, todays ammo would set you on your can real fast, I would not want to drop the hammer on two rounds of 3 1/2 Nitro turkey load, one is about all the punishment I care to endure, on that same note I should mention that if you were to use todays ammo in one of these old guns there is a good chance you could be severly hurt or killed as they are more than likly to explode in your face, They were not built for that kind of pressure!!!Are there barrels made specifically for slugs? Why? Also, are there shotguns that have one barrel for slugs and one for regular ammunition? Is the kick alot more if you fire those both at the same time?