[Skipper]

I'm doing some ballistic tests for a college Prof. in a Forensics course.
Can anyone tell me the bbl. twist rates for a S&W 647 and a Colt Agent?
Help appreciated.

Skip

[BlindJustice]

Here's something for you and the professor to wrap your brains around.

Colt 1911 Semi-AUto in .45 ACP full size barrel is rated at
5 inches, which includes the length 0.898 inch so the rifleing is
essentially 4 inches. The rifling twist is 1 in 16 inches

S &W .45 ACP Revolvers with a 5 inch barrel have a full 5 inches
of rifling, the cylinder isn't part of the barrel lengh. The
rifling in the revos have always been 1 in 15 inches,

SO, in the 1911 the bullet gets 1/4th of a roatation
& in the Revo it gets 1/3rd of a roatation, & one other
thing one is LH twist & the other is RH twist.

Now, determine if this makes a difference in the
southern or northern hemisphere.

Maybe the answer is Academic...

[Jim Watson]

Most Colt .38s have 14" twist. S&W .38s are usually 18 3/4" the opposite hand.

[Archie]

I remember Colts' rifling spins one way (clockwise or anticlockwise) and S&W spins the other. I also remember the rifling twists are close to each other, but not identical. I also remember some firearms have five lands and grooves and some have six. Some have eight, for that matter.

I betcha part of what your instructor is trying to teach you is the value of good reference material and how to find out what you need to know. (Albert Einstein once said he never memorized anything he could look up.)

There are several reference books that have this information. The older Speer reloading manuals have some of this information in tabular form. I think the Lyman reloading manuals have some of this information.

If you are going to be doing firearms forensics to include ballistics recognition and interpretation, you might want to explore "Cartridges of the World" and other books of that ilk relating to current and historical firearms.

When I get home tonight (and if my aging brain and memory hold up) I will check the close references I have.

You might also do a Google search for 'firearms twist rates' and see if you come up with any relevant answers.

Good luck.

[Skipper]

Thanks fellows,
The professor is actually my stepson and I'm not a student, just the "gunny" he turned to for help with this project.
Thanks for your help. I'll take all the credit.:D

Skip

[mnw42]

Colt used 1:14 twist with all of their .38/.357 revolvers, if I recall. I'm sure a call to Cindy at Colt and Smith and Wesson would answer all of your questions

[mnw42]

oops!

[keyboard commando]

From Hatchers' Textbook of Pistols and Revolvers: pg.14..... Colt; All center fire calibers,6 grooves left hand twist, one turn in 16 inches.I am not familiar with the S&W 647 or the .17 cal.

[Skipper]

Sorry man, I meant 637, not 647. .38 special,just as the Colt is. :o

Thanks,
Skip