[Harvster]

I was just looking at the rifling in my S&W 642 and noticed that it can't be more than a sixth of a turn or so. Does this really impart much spin on the bullet? Do they ever measure rotational speed of bullets and correlate it with trajectories etc.?

[Koos Custodiet]

Let's say your muzzle velocity is 600fps or so, and it's a 2" barrel (hey, I'm guessing here). That's a full turn in 12", which happens to be a foot. That means your bullet is spinning at 600 revs per second, or 3600 rpm...

Edit : BTW 600fps is low but it makes the math easier :-)

[Vern Humphrey]

Yes.

The effect of rifling pitch (and rate of rotation) has been studied for about 500 years. Pistols generally shoot short bullets, which don't need a lot of spin to keep them stable.

But if a pistol has a quarter turn in 4" of barrel, that's 1 rotation in 16 inches of forward movement -- which is identical to the standard for the .22 Long Rifle. If that same gun has a muzzle velocity of 800 fps, that's rotational rate of 6,400 rpm.

[rcmodel]

The only time your snubbie won't be spinning up it's bullets to full rotational speed is if a soft lead bullet strips out in the rifling.
That will lead to severe barrel leading, accuracy problems, and in some cases, bullets key-holing on target.

It can happen in longer barrels, with hot loads driven too fast for the lead bullet alloy.

It is generally never a problem with jacketed bullets in any firearm, and very seldom if ever a problem with .38 Spl. lead factory loads in a S&W snubbie.

If you can recover some of your fired bullets, you will see very sharp & distinct rifling marks on them, indicating they had to be spinning as intended to make it through the barrel without stripping the rifling.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

[DBR]

600 RPS is 36,000 RPM