What is the NFA definition of rifling?

[Caliper_Mi]

Ok, so I understand the whole rifled/smoothbore pistol thing as it relates to AOW's. I'm curious what the NFA defines rifling as.

Here's my thought: many muzzleloaders have rifling twists as slow as 1:66 or 1:70 because the roundball doesn't need much twist to stabilize. What if one stretched this out to, say 1:500 rifling? One could construct a pistol with such rifling and have a rifled bore, but not impact shot pattern so much if firing a shotshell through it due to the low rate of spin.

What if we really stretch the idea out to straight rifling? (1:infinity twist ) I realize this stretches the definition of rifling since it imparts no spin on the projectile, but it would be difficult to argue it is a smoothbore either.

I couldn't find anywhere that this is answered, but just wondering if there is another hole to exploit in the NFA. Plus, something like this could make the Defence Distributed Liberator not an NFA item...

 

[25cschaefer]

Look into Forsyth rifling, it uses shallow wide grooves, often in the 1:125" range. It was developed for muzzle loaders to stabilize big bore round balls at high velocity (12bore at 2000ft/s) and users say it does not mess with shot patterns.

 

[45crittergitter]

I've wondered about this as well - I'd like a Taurus Judge with straight rifling.

 

[Jim Watson]

Example:

Back when the TC Contender .45-.410 was relatively new on the market and selling well, but at a rather high price, Walter Craig brought in a bunch of shot pistols on very cheap Brazilian .410 shotgun actions. They were legal because they were rifled and the chamber would accept .45 Colt. They were obvious loophole guns because the rifling was nearly straight and very shallow. He was doing a good business in them when the feds took notice.

In order for them to stop the importation of those cheap guns, they also had to shut down TC with their nice guns. For a time, TC could not sell a .410, so they offered their Hot Shot guns, same performance as a .410 but with shot in a plastic capsule in a regular brass pistol case. I think in .357, .44, and .45. Gunsmiths did a good deal of business rechambering the .45s to .410, which was not actually illegal, just discouraged by a jawboning government agency.

The feds eventually relented and you could get TC .45-410s again. Also a pistol-carbine conversion barrel and stock, which they opposed at one time.
Walter Craigs cheapies did not return, though. You have to get a Snake Charmer or knockoff with 18" barrel and vestigial stock for 26" OAL.

Which does not say whether you could manufacture a shot pistol with straight rifling, but indicates you could probably get a way with if for a while.

 

[JustinJ]

I must admit i'm fairly ignorant in shotgun loads but would it no be possible to create a projectile with counter rifling to the bore that will cancel out?

 

[25cschaefer]

No, the projectiles, in order to not destroy the rifling, need to be softer than the barrel and will therefor be acted upon by the rifling. If the rifling is shallow and a very slow rate of twist it will have negligible effect on the shot pattern, especially if a shot cup is used.

refer to the bottom half of this page:

http://underhammers.blogspot.com/