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Discussion in 'Gunsmithing' started by nraman, Feb 7, 2010.
What is the minimum twist that will stabilize a 9mm 147gr bullet at around 1000fps.
1 in 16 is used by a number of 1911 makers and somewhere around 1 in 10 on many foriegn guns. At typical pistol shooting range (less than 30 yards), it really doesn't matter.
I know that, what I don't know is the minimum twist that will work with the 147gr 9mm. Some aftermarket barrel makers use 1 in 20 or more.
If you are serious about only the 147 at 1000 FPS, I would go with the 1 in 10 twist.
I would if I had the choice. That's the reason I am asking if anybody knows the minimum twist that will stabilize the 147gr. You see KKM has some super slow twists like 1x20 or 1x22 and they say that it is fast enough, to me it seems way too slow. They only have two choices and both choices are slow.
Just read your post. I have a buddy that used to be an armorer at Quantico and built match pistols for the Marine Corps pistol team.
He and I have discussed that very thing (9mm barrel twist), and if I remember correctly, he said that slow of a twist for 9mm as offered by KKM was excellent and they got some phenomenal groups. I think he also uses a lot of their barrels now, and KKM may be the company that advised them to use it when he was on active duty.
I'll check with him tomorrow on bullet weight and get back to you.
Phil Jones (pmj)
I appreciate your efforts and look forward to getting the information. KKM has two twists, one for lightweight bullets and the other one for the heavy.
Another problem I ran in to is trying to measure the slow twist of a pistol barrel. I have no problem measuring rifles but, when it comes to pistols with a twist as slow as 1X18 or slower, I cannot come up with a reliable way to measure it.
I'll also ask him about a method to check the slower twist rates for instances like this.
The Miller Ballistic Stability Formula was used to calculate all following values:
A rate of twist slower than one turn per 32.89 inches will fail to stabilize gyroscopically a 9mm 147 gr. JHP with a length of 0.655" @ 1,000 fps.
Some other gyroscopic limits if you are interested:
9mm 115 gr. (0.595") @ 1,135 fps = one turn in 33.53 inches
9mm 124 gr. (0.610") @ 1,100 fps = one turn in 33.58 inches
.45ACP 230 gr. (0.640") @ 850 fps = one turn in 48.80 inches
Hope this helps you out,
I forgot to thank you when you posted the info.