147 Gr Lyman 9MM - Faster or slower twist rate?

[robertbank]

Ok I have two barrels for my 5" M&P Pro. Both are factory. One is 1 - 18 that came with the gun originally and the other is a 1 - 10 twist factory barrel that the gun comes with now.

I have had problems in the past with bullets tumbling. Which barrel should be the best to stabilize the 154gr bullet. Bullets are sized .357. Vel. is 860fps

Take Care

Bob

[Outpost75]

The faster twist should be better with the heavier bullet IF it "fits." Undersized bullet will still tumble. Have you tried .358" and will they chamber in your gun?

[robertbank]

The faster twist should be better with the heavier bullet IF it "fits." Undersized bullet will still tumble. Have you tried .358" and will they chamber in your gun?

I get excellent accuracy out of both barrels using 125 gr bullets at .357. Sized at .357 with either bullet are very tight in in the bore with no leading. I may load a few at .358 to see if there is any difference. I will stick to the 1 -10 twist barrel thanks for the reply.

Take Care

Bob

[tazman]

I agree that the faster twist barrel should work better with that boolit.

[robertbank]

Well when you hear from two well respected board members who both agree then you can pretty much seal the deal. Thanks guys, I always get the fast vs slow heavy vs light mixed up.

All the best

Bob

[35remington]

Just to throw some sand in the gears, I will note Smith 38's stabilize 158's at even lower velocities than you are getting with 1-18 3/4" twists.

If the bullet tumbles I would suspect fit more than twist. 154 ain't that long of a bullet.

FWIW.

[tazman]

Just to throw some sand in the gears, I will note Smith 38's stabilize 158's at even lower velocities than you are getting with 1-18 3/4" twists.

FWIW.

What you say is true. I still think Robert's faster twist barrel will do a better job with the heavier/longer boolit.

[35remington]

I would wager other factors such as barrel fit to gun and bullet fit to barrel will be far more operative. 1-18 should be a gracious plenty with a 154. Since Smith revolvers will outshoot plastikpistoles of most all varieties, I highly doubt twist is limiting here.

[tazman]

I seem to remember the Colt revolvers with a slightly faster twist than the Smith's out-shooting the Smith revolvers on regular basis. Even to the point of people putting a Colt barrel on a Smith frame.
Do I remember incorrectly?

Also, most semi-auto pistols simply don't ever shoot as well as a revolver due to the clearances required for the parts to operate where a revolver has a fixed barrel(fixed barrel autos being the exception).

I own only one centerfire auto that will shoot as accurately as my revolvers. That one being a tightly fitted 1911. Definitely not a plastikpistole.

[35remington]

If shooting wadcutters slow the Colts had some advantage over the Smiths in reducing bullet yaw. This is not the case here so it is not relevant. If twist was limiting my Smiths would shoot worse than they do. At the 860 fps RB is discussing 1-18 is plenty of twist. I already acknowledged loose autopistol tolerance fit is way more limiting than twist here.

[tazman]

I guess we will just have to fail to agree on this.

[35remington]

Taz, 1-18 3/4" twist has been the standard twist for Smith for 120 odd years and was fine to stabilize 158's at 750 fos and even slower. Smiths have a wonderful reputation for accuracy in 38 Special. If 1-18 3/4 twist was inadequate surely it would have showed up by now.

I do have considerable foundation for claiming 1-18 is really not limiting with mentioned bullet weights here. Disagree with me and Smith as you wish.

[tazman]

I didn't say that the 1-18 twist was inadequate. I said the faster twist should do a better job. Not the same thing.
Most of the factory 9mm barrels I am familiar with have faster twist rates than 1 in 18. Even S&W has decided to use a faster twist in their current M&P Pro according to the original poster.
Perhaps Smith changed their mind about that slow twist, at least for the 9mm cartridge.

[35remington]

The 9mm is pretty universally acknowledged to have a vastly faster twist rate than it really needs or has to have. Even 35 rifles like the 35 Remington are only 1-16 and shoot a much longer bullet. Such rifles shoot well with 158's at quite low speeds.

Once a bullet is adequately stabilized, spinning it faster will not increase its accuracy, especially in light of all the other factors that are limiting in a pistol. A better job? How? We are already well above what is necessary in terms of bullet stability.

Positing that a 1-10 twist will be "better" than a 1-18 is probably only provably relevant for lower speeds and heavier bullets than discussed here. As I said, 1-18 3/4 is enormously well proven. To expect a 154 grain bullet shot out of a 1-18 twist at 860 fps to be lacking in some way is unrealistic given what is already well proven to work very well.

[tazman]

As has been said elsewhere on the site-- Everything is theoretical until the trigger is pulled-- or at least something like that.
It will be interesting to see how this all plays out for Robert. It wont be theoretical anymore for him. His results are all that are going to matter for him.
My S&W 929 revolver has a 1 in 10 twist and shoots all the boolit weights well.

[35remington]

As I said, twist rate may be vastly overshadowed by other factors. Just because something happens does not mean it happens for the reasons we think it does. Some other factor or factors may be the real cause of any observed differences.

In any observed results we have to give all the possible explanations for those results their due, not just the ones we feel like focusing on.

[robertbank]

Listen the M&P Series were not noted for their accuracy and S&W finally changed their 9MM barrels to 1 - 10 twists. I bought the 1 - 10 barrel and accuracy was improved using 124gr bullets for certain. I know the smith 38's had the slower barrel twist but the 9MM is not the 38spl.
Virtually all European guns have 1 - 10 twist barrels. It maybe that in the US it is "Universally" thought the 9MM doesn't need the faster twist but the US is not the Universe and most 9MM from offshore use a 1 - 10 twist or the metric equivalent. S&W didn't make the change on a whim, their M&P 9MM pistol had some accuracy issues. Since the change you don't hear the comments quite so much.

Maybe it has something to do with the slightly smaller diameter of the 9MM barrel .355 vs .357

Take Care

Bob

[tazman]

Good point

[35remington]

Given how short 9mm bullets are, and given short bullets need less twist than longer ones, I would suggest any accuracy improvements have more to do with possible exterior dimensional changes that affect barrel fit than twist. Such has been considerably discussed with some gunsmiths that work on such pistols that I know.

Their contention was that they could measure clearances on the barrel/slide fit and predict pretty well beforehand how well the pistol was going to shoot. As I said, we must be careful not to give credit to one factor while ignoring the likely much more significant contributions of other factors.

Perhaps one needs to check the barrel twist rate of Bar-Sto 9mm barrels.....then ask why they shoot so well? For some reason the maker of match grade barrels decided the 9mm was fine with a much slower twist than 1-10.

Also a good point!

[Tackleberry41]

I use that same lyman 147 grain in several guns. Browning HP, S&W shield, Kel Tech carbine, 357 sig, works in everything so far.