Mathematical Challenge re: CE 399

[Bob Prudhomme]

how many inches this bullet would have to travel, in the barrel it was fired from, in order for it to make one complete revolution?

Hi Bob..


Isn't a full rotation defined by the barrel itself... the grooves in the barrel complete 4 rotations,or something like that? or is it a 4 groove barrel with an unknown number of rotations?

The distance between these complete rotations within the barrel will give you your distance since it does not matter whether the bullet falls out of the barrel or is shot out,
.... the bullet wouldn't rotate at all without those grooves I imagine...

So I looked up rifling and found this on wiki: do we know the Twist Rate of the MC?
DJ

Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis. This spin serves to gyroscopically stabilize the projectile, improving its aerodynamic stability and accuracy.

Rifling is often described by its twist rate, which indicates the distance the rifling takes to complete one full revolution, such as "1 turn in 10 inches" (1:10 inches), or "1 turn in 254 mm" (1:254 mm). A shorter distance indicates a "faster" twist, meaning that for a given velocity the projectile will be rotating at a higher spin rate.

http://en.wikipedia.org/wiki/Rifling

Yes, David, those definitions are correct. A rifle barrel that has rifling grooves with a 1:10 rate of twist means that the bullet will make one complete rotation in the space of 10 inches of the barrel's length. It will leave the distinctive rifling marks, as seen on CE 399.

However, different rifles have differing rates of twist in their riflings, as well as the "lands and grooves" being of varying widths. It is not uncommon, in sporting rifles, to see rates of twist vary from 1:7 to 1:12. Naturally, the tighter twist will leave much tighter rifling marks on a bullet. As CE 399 is the evidence presented by the WC, I am attempting to establish the rate of twist of the barrel it was fired from to see if it matches the known rifling specs for Carcano rifles.

P.S. Yes, we know the rate of twist for Carcano barrels. It will vary, in a short barrel, depending on which rifle it was. See the final post in my thread "Request for Help to ID Rifles" and you will likely understand why I am so interested in determining the rate of twist of the riflings in the barrel that fired CE 399.