I am assuming what he meant by the smooth but rifled bore is...... this model of contender barrel is one that has a smooth bored barrel but has a rifled screw in choke for shooting the 45 Colt rounds. Thus you are able to shoot shot through it with conventional chokes and 45 Colt with the rifled choke.

This barrel will fire the 45 Colt rounds because the .410 shotgun shell (brass head) is the same diameter as the 45 caliber bullet and this barrel does not have a forcing cone to reduce the diameter of the bore like a conventional shotgun barrel does. It is the same diameter all the way through the barrel.

A side note about this gun is that you should NEVER fire rounds such as the 454 Cassul and 460 S&W mag, even though they would easily fit in the chamber, due to the fact that they are high pressure cartridges and would destroy the gun and possibly injure the shooter and bystanders. The 45 Colt operates at only 15,000 cup where as the other two operate at 55,000+ cup.