How is the .50 Bore Limit Measured By The ATF?

[Loyalist Dave]

Hey folks, how does the ATF determine the "bore" of a firearm is over .50 inches, and is therefore prohibited without NFA approval of the owner? Is it measured at the muzzle? I ask as somebody suggested that Taurus take their newest monstrosity in "28 Gauge" and taper the bore from say .60 at the forcing cone to .50 at the muzzle, and at the same time offer a short shell with a .495 slug, as well as a multi-ball load with say 3 .490 lead round balls. A shot column fired from a standard shell would compress as it reached the muzzle, but the slug or round ball would sorta rattle a bit then calm down as they reached the muzzle. Just wondering.

LD

 

[oneounceload]

Bore diameter - a simple tool does an excellent job - down to the .001

 

[LiENUS]

I think the best measure is that they measure it arbitrarily

 

[Sam1911]

I ask as somebody suggested that Taurus take their newest monstrosity in "28 Gauge" and taper the bore from say .60 at the forcing cone to .50 at the muzzle

Seeing as the Rampaging Judge was not declared a Destructive Device as the recent errornet buzz predicted/reported, this probably won't be an issue.

http://www.americanrifleman.org/blogs/quashing-raging-judge-rumors/

 

[Loyalist Dave]

Bore diameter - a simple tool does an excellent job - down to the .001

Yes my original post recognizes it's "bore diameter", the question is do they measure it at the muzzle [say with a micrometer as many of us do], or perhaps they measure the entire length of the barrel?

Unfortunately, the ATF is not the only hurdle a handgun must get across in the People's Republic of Maryland.

LD

 

[CYANIDEGENOCIDE]

I am pretty sure the ATF uses a .500 slug and the try to fit it into the barrel. I vaguely remember when the .500 S&W came out it was supposed to be .510 just like the .50 BMG. But when the design was submitted for ATF approval the slug fell straight through the barrel. So back to the drawing board and the .500S&W is a true .500 inch

 

[highorder]

I am pretty sure the ATF uses a .500 slug and the try to fit it into the barrel. I vaguely remember when the .500 S&W came out it was supposed to be .510 just like the .50 BMG. But when the design was submitted for ATF approval the slug fell straight through the barrel. So back to the drawing board and the .500S&W is a true .500 inch

Close. The ATF does use a plug gauge, but that anecdote actually refers to the creation of the .50AE cartridge designed for the Desert Eagle.

 

[ilove2shoot]

so if I wanted to make something using a 50BMG projectile in a .510 50BMG barrel.....I need to get ATF approval first? Looking at doing a sub-sonic only project.....

 

[GrimmLV]

28ga. is .55 just FYI

 

[Ranb]

so if I wanted to make something using a 50BMG projectile in a .510 50BMG barrel.....I need to get ATF approval first? Looking at doing a sub-sonic only project.....

Take a look for the 510 whisper and other subsonic cartridges. It uses the same bullets the 50 BMG uses, but with about a 30 grain powder charge in a 1.885" case made from the cut down 338 lapua. No ATF approval needed as it is still equal to or less than a half inch bore. My 510 whisper Encore sounds like a car door slamming with the silencer attached. Shooting tracer and API makes it more interesting.

The ATF measures at the tops of the lands. So the 50 BMG which shoots .510" bullets is .500" at the lands and .510" in the grooves as it has .005" deep grooves. It is really the 51 BMG as measured by the conventional standards of the USA. The 30 caliber barrels made in the USA are .300" at the lands with .oo4" grooves, so they shoot .308" bullets.

The 303 British (think Enfields) is .303 at the lands, .311" at the bottom of the .004" grooves and shoots .311 bullets.

Try to insert a .500" steel slug into a barrel, if it fits in, then it requires an ATF exemption or a $200 tax paid. Sporting long arms like 20 gauge and most higher shotguns enjoy this exemption.

Ranb

 

[Sam1911]

Sporting long arms like 20 gauge and most higher shotguns enjoy this exemption.

And .600 Nitro Express. And JD Jones' cool 14.5mm JDJ wildcat! (You know, for when you want to ditch that .500 Whisper and get serious!)

 

[Ranb]

I have a 50 BMG LAR, is that serious enough? I will make a silencer for it some day, or for its replacement. Shoot the 510 whisper with a 953 cast bullet and no can. In a 7.5 pound gun it hurts a bit, after three rounds it hurts more than a bit hahahaha.

I've looked at the 14.7 jdj, but I am too cheap to invest in it.

Ranb

 

[ilove2shoot]

Ranb,

Thanks for the clear answer answer. I know about the whisper cartridges. I play quite a bit with a semi auto 30 sub-sonic setup right now.....I am working on something kinda along the lines of a 510 whisper, except I want it to cycle a Semi-auto magazine fed weapon.

 

[CleverNickname]

And .600 Nitro Express. And JD Jones' cool 14.5mm JDJ wildcat! (You know, for when you want to ditch that .500 Whisper and get serious!)

From all the examples I've read, it seems that the ATF will give out a sporting purpose exemption for pretty much any rifle cartridge over .5", if someone applies for it, as long as it's never been used in a firearm fielded by a military.

 

[ilove2shoot]

also gotta consider that most (if not all) of these big bores are bolt actions rifle. kinda hard to argue that a bolt action rifle is not a sporting rifle.