How a Popular Misconception Gave Away a Lie by the FBI

[Bob Prudhomme]

The only way to tell if this rifle has standard twist rifling or cut down progressive twist rifling is to do a sulphur cast of the inside of the barrel at the muzzle.

Think they would lend us C2766 for the weekend?

I think that Frazier did a sulphur cast. Let me see if I can find an image of that.

Yep. CE 540.

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The cast starts at the throat, right? I'm no expert, but I'm guessing thats not a progressive twist.

IIRC Frazier testified that the rifle was 7.35 rebored for 6.5mm. Does that help us in any way, assuming he's telling the truth?

A sulphur cast can be done from either the throat or the muzzle of the rifle, for various reasons. They are often done at the throat to get a reverse model of the cartridge chamber.

CE 540 is a rather odd sulphur cast, as I seem to recall Frazier testifying that a cast was made of the bullet chamber, as well. What makes you think that is not a cast of progressive twist rifling?

It is a popular myth that 7.35mm short rifles were re-bored or re-barreled to 6.5mm. The majority of 7.35mm short rifles were sold to Finland and used in their war against the USSR. Think of it for a second. How can you rebore a rifle from a larger calibre to a smaller one? There are cases from the First World War where old 10.35mm M1870/87 Vetterli Vitali rifles from the 19th Century were converted to 6.5mm by having a liner tube welded to the inside of the barrel, but this was never the case with the M91/38 short rifle.

As I've said before, Frazier was not a source for accurate information.