No, the largest caliber for infantry rifles is .50 caliber (12.7x.99mm in NATO). Besides a .54 caliber gun is WAYYY to big to have a person fire with todays advances in gun-powder and weaponry. However the M1A1 Abrams battle tank has a 120mm SMOOTHBORE cannon. Also, the A-10 Warthog has a 30mm minigun in it's nose.
Around the mid 1500s. Most would continue to be smoothbore for another 250 years- they were expensive to make, difficult to load.
He would make barrels. Everything was shipped and stored in barrels.
Generally a smoothbore weapon, some rifledbore flintlock pistols were produced. The smoothbore were easier to make and mass produce at a faster rate.
Well there is no Remington Model 12 shotgun, a model 12 is a 22 lr, they did make a smoothbore but it would have said so. A smoothbore model 12 is rare and valuable but I doubt that's what you have if it doesn't say smoothbore it's probably shot out.
Seven barrels
barrels
Since the 9200 series seems to have been discontinued in 2001, I doubt if they are still making extra barrels, but it is possible. The gun was available with 18.5, 22, 24 (rifled and smooth), and 28" barrels. A gunsmith should be able to find some, or you can try contacting Numrich Gunparts.
Coopers make barrels.
Coopers
A cooper makes barrels.
on average 1.6 million barrels per day
Pistol barrels range from 2" to 12", and almost every increment in between. Longer barrels increase accuracy, shorter barrels make for more compactness.