All smooth-bored bbls are required by law to be a minimum of 18" in length. All the "Legal" guns firing a .410 (or other shot-cartridges) have rifling in them. An original LeMatt would not fall under this law as it is muzzle loader, not a cartridge gun. The old Stevens Tip-Up, H&R Handi-Gun, Marble Game-Getter & the Ithaca Auto-Burglar etc all fall under this category & were required to be registered by the National Firearms Act of the 30's. I was thinking 1934, but it may have been '33. A transfer tax is required every time one is sold. At some point in time, I think it was shortly after the '68 Gun law took affect a grace period was given & anyone who owned one of these without registration could register it for a fee of, as I recall $50.00.
If you set up & simply bore the rifling out of an ordinary revolver bbl, such as a .45 Colt You have converted it into an "Illegal" "Sawed Off Shotgun". Some years ago Harvey Donaldson tried to set up a buisness of doing this, thinking it would be legal as they did not fire ordinary Shotshells, but was ruled against & had to cease.
A Muzzle attachment can be applied to eliminate or minimize the effect of the rifling & the gun remain legal, or most of the bore can be smoothed, leaving only a "Rifled Choke" & it remain legal, but it Can't be "Smooth All the Way". So much for the BATF's "Logic"
