9MM twist rate


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fecmech
October 26, 2004, 10:46 AM
Gentelmen--I don't ever remember reading why the 9MM was designed with a 1 in 10 twist. Does anyone know why it has such a fast twist, particularly since other .35 cal rifles and pistols run 1 in 14 thru 1 in 18?. Nick

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cratz2
October 26, 2004, 01:28 PM
Hrmm... never really thought about it. Probably something to do with the lower velocities and lighter/shorter bullets in handguns vs rifles.

fecmech
October 27, 2004, 09:58 AM
I've been trying on a number of boards to find out what the logic was for the fast twist. Generally the longer and heavier a bullet is the more twist required to stabilize it. .38/.357 with a longer/heavier standard bullet @158gr twists run 1in14 thru 1 in 18, and it appears to me 1 in 20 or even less would stabilize the short 115-124gr bullets that were standard when the cartridge was designed. .35 cal rifles which shoot bullets in the 200 grain range seem to do just fine with 1 in 14 twists so I'm curious as to why the 9mm ended up with such a fast twist. Nick

mete
October 27, 2004, 10:43 AM
One list shows Colt with 1 in 16" and S&W 1in10", My HK P7 is 1 in 10". If you knew how accurate the P7s are you wouldn't worry about it !!!

Lone Star
October 27, 2004, 02:16 PM
I think many European 9mm's use a faster twist.

All else being equal, barrels with faster twist tend to expand bullets better. This can be viewed most easily by firing bullets from S&W (1:18.75" twist) vs. Colts with 1:14-inch twist) .38's or .357's.

Usually, even if the velocity is a little lower, the Colt-fired bullets expand better.

The late John Jobson once noted in, "Outdoor Life" that he had two .270's. One had a "ten-twist" barrel; the other a 1:12 twist. The faster twist barrel made a greater mess of woodchucks shot with it.

Lone Star

blackpanther
October 27, 2004, 08:57 PM
1 in 10 is the optimum for the 124gr which is the original design.One other thing is all
the 9mm cases now are under sized from the original specks.

Ed

Jim Watson
October 27, 2004, 11:59 PM
I doubt there was any consideration of expansion when the 9mm P came out in 1902.

Ed Harris once got Barsto to make him a BHP barrel with 18 3/4" twist out of a .38 Special blank. It was more accurate than the standard Barsto 16 twist and a lot better than the factory 10 twist.

Schuemann is making a 32 twist for Supers with 135 gr or lighter bullets.

So I fail to see how a 10 twist is optimum for a 124 grain bullet.

I still think as I said in another thread on the subject, that they set the twist four turns per metre just to be on the safe side with a new caliber and it was rounded off from 9.85 to 10 inches in English Make. Or maybe they actually made it one turn in 240 mm, 9.34" like the 8x57 Mausers. I no longer have a real Luger to check it on.

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