Barrel twist rate and accuracy

[LiveLife]

Glock lists barrel twist rate of 1 in 9.84" for their barrels except 1:15.75" for 45ACP/45GAP and 1:15.98" for 357Sig.

Most aftermarket barrels use 1:16 twist rate except for KKM which has slower twist rate of 1:20 (but I read KKM can go slower at 24 to 32 but have not verified this) and Wilson Combat used to be 1:10 but twist rate is now 1:16:

Bar-Sto - 1:16
Briley - 1:16
KKM - 1:20
Lone Wolf - 1:16
Storm Lake - 1:16
Wilson Combat - 1:16 (was 1:10)

Some have posted accuracy issues with M&P9 and Hilton Yam expressed the problem may be attributed to 1:18 twist rate and S&W changed to around 1:24 in this comparison article - http://modernserviceweapons.com/?p=159

But looks like S&W changed the M&P9 twist rate again to 1:10 with improved accuracy on par with Glock (1 or 2 dimples on the bottom of barrel lug) - http://modernserviceweapons.com/?p=3719

Since my experience is limited to M&P40/M&P45, I can't speak about M&P9 but my factory Glock 22 has produced tighter shot groups than factory M&P40 (my M&P45 will leave both in the dust but it has a trigger job).

For one thing, range tests I have done with lead/plated bullets seem to favor the slower 1:20 twist rate - http://www.thehighroad.org/showthread.php?t=745656

What's your feeling on barrel twist and accuracy?

 

[Jim Watson]

I think that rifling twist rate is way down the list of factors in service pistol accuracy.
S&W is floundering in the dark with the Plastic M&P 9mm. The dimpled barrels are likely shooting better because they fit the gun better, not because they have a different twist rate.

 

[Clint M]

Unless yo are tailoring the twist to one bullet for competition, or a lead bullet etc I don't think twist rate plays any role in accuracy other than to stabilize the bullet. Extreme twist rate on either end will of course be a different story.

Edit= I shouldn't have said any, twist rate versus accuracy can't be proven in say 5 barrels with different twist rates due to differences in all the things that go into making the barrel, and the tool work to finish it. I'm not sure how large a selection of barrels you would need to determine the difference in accuracy ?

 

[Seabeeken]

Perhaps this topic should be under gun smithing rather than reloading

 

[Clint M]

I reckon the OP is possibly looking at purchasing bullets and looking at weight, barrel twist etc looking for that perfect bullet that will do one hole (with more than one shot). Seems twist rate, bullet weight comes up often in the handloading forum, and over the years it seems barrel twist versus accuracy has started spreading myths that are just internet myths. I assume it started with the advent of the 69gr SMK when many barrels wouldn't stabilize it, from that point on it went from twist rate to stabilize a certain bullet weight to twist rate is more accurate.

It's easy to get side tracked when researching I may have once or twice myself. I may be dead wrong on the way twist rate vs accuracy myth was started, whatever the reason it is wide spread by now.

 

[Jim Watson]

The many mutations of the .223 have lead to an exaggeration of the significance of rifling twist rate in most cases.
If you are an ambitious rifle shooter, you can gain a little by twist optimization.
I don't know how good a pistol shooter you have to be for it to matter, but it is way on up there. What twist does David Sams put in NM Berettas?

 

[GLOOB]

In a rifle too fast a twist can limit what kinds of bullets you can shoot. Varmint bullets can self destruct. Cast bullets can have lower max speed. But in a 9mm pistol it doe's not matter much. It might take the bullet a bit longer to stabilize after leaving the muzzle. that may or may not show up on the target at longer ranges.

 

[Saleen322]

The faster twist is the safer way to go for a service gun; Glock, etc. They tend to shoot a wide range of bullets at least acceptably accurate. A target gun will generally have a slower twist to shoot a much smaller range of weights but will almost always get better accuracy than the service guns with bullets in that range.

 

[tipoc]

Saleen is correct.

When Georg Luger built the first guns in 9mm he set the rate of twist at 1 in 9.84" which is a relatively fast rate of twist and does well with either jacketed or lead bullets doing between 1100-1200 fps in a range of bullet weights between 90-125 or so and even 147 gr. bullets can do quite well. This rate of twist does quite well in a service side arm.

Most manufacturers use this for the 9mm.

S&W used this rate of twist in their 9mm pistols (as did Colt) through their first-third gen semis. When they introduced the S&W M&P line for some reason they went to a faster rate of twist and accuracy suffered. It was a rate of twist more in line with target guns and quite specific bullets than with service or defensive sidearms and factory fodder.

The rate of twist varies from caliber to caliber and a number of factors effect it. The diameter of the bullet, the material of the bullet, the speed and others. For example the rate of twist for 38 Special is different than for the 9mm.

Schumann barrels makes barrels for specific match needs of competitive shooters. Some of the considerations they take up are discussed at their web site.

http://www.schuemann.com/Portals/0/Documentation/Webfile_Barrel Twist Rate.pdf

tipoc