9mm Barrel Twist Thoughts/Questions

First topic message reminder :

I'm not a professional gunsmith.  But I enjoy both shooting and tinkering with guns.  Over the years I have built a half-dozen or so wadguns that were accurate, reliable, and had fairly decent triggers.  Since I have a small machine shop I have also built a number of jigs and special tools that facilitate some of the jobs, such as barrel fitting and trigger work.  I've concentrated on accuracy and feel especially gratified when a gun I have built shows good accuracy.  Recently I have been considering playing with 9mm on the 1911 platform; not so much as a bullseye centerfire gun but just to see if I can build an accurate one.  Along that line I have had some thoughts and done some calculations (I'm an engineer but not a ballistician) on 9mm barrels.  Anyone is welcome to chime in here, but I'd especially welcome the thoughts of Jerry, K.C. and others who have struggled with the 9mm accuracy problem.

My starting point is the famously accurate 38 Special 148gr HBWC round out of the really good PPC guns, which pretty much all seem to use barrel twists of 10-12".  The Remington Targetmaster 148gr round runs about 770 fps, and out of a barrel with 12" twist is spinning 46,200 rpm at the muzzle.  Since that round is so accurate, my thought is that the 147gr 9mm bullet, which is only .002" smaller in diameter than the 38, should also be accurate if spun at the same rate.  Unfortunately, to get the 147gr bullet up to that rotation using common 16" twist 9mm barrels requires a muzzle velocity of about 1026 fps, which is nearing a maximum load and certainly would not qualify as low recoil. Essentially, my thought is that if we had match quality 9mm barrels with a twist of 10-12", we could push something like the 147gr XTP at a speed of only 750-800 fps with the fast spin (46,000+rpm) needed for accuracy, and yet have a relatively soft recoil.  In fact the 147gr 9mm bullet and the 148gr 38 bullet pushed at the same speed would have essentially the same "calculated" recoil impulse.  I know the "felt recoil" would be different because the case capacities are different, but they would be close.

At the risk of damaging my own argument, I will note that I am aware that some of the most accurate 9mm ball guns are using the KKM 32" twist 9mm barrel and a 115 grain bullet.  Even at a blazing 1200 fps that barrel is only spinning the bullet 27,000 rpm, which I guess must be enough to stabilize that short bullet.  But frankly I am puzzled that the slow twist works so well on even the short 115gr bullet.

What do you 9mm 'smiths think?  Am I off track here?

k.c.
What barrel and twist are you using for the 9mm and 115 gr XTP?

I am new to the forum but not new to the bullseye sport.  I have nice 38 super 1911 race gun that I am going to make into a 9mm with a 5 inch bushed barrel.  I am going with a Kart barrel.  I will post the outcome when I test it.  If it will group under 2 inches at 50 with factory Atlantic Arms 115 gr I will be good to go, if not I will drop back 10 and punt.

Dr.Don wrote:k.c.
What barrel and twist are you using for the 9mm and 115 gr XTP?

Not KC but, one of the 9MM is headed my way!   KKM barrel 1-32.

- Dave

I've been digging around and it looks like Bar-Sto is still my only option for a SIG P226 barrel. My preference IS for one I will have to fit rather that drop in. Anyone have or hear reports on how the Bar-Sto 9mm P226 barrels do???

Dr.Don wrote:I'm not a professional gunsmith.  But I enjoy both shooting and tinkering with guns.  Over the years I have built a half-dozen or so wadguns that were accurate, reliable, and had fairly decent triggers.  Since I have a small machine shop I have also built a number of jigs and special tools that facilitate some of the jobs, such as barrel fitting and trigger work.  I've concentrated on accuracy and feel especially gratified when a gun I have built shows good accuracy.  Recently I have been considering playing with 9mm on the 1911 platform; not so much as a bullseye centerfire gun but just to see if I can build an accurate one.  Along that line I have had some thoughts and done some calculations (I'm an engineer but not a ballistician) on 9mm barrels.  Anyone is welcome to chime in here, but I'd especially welcome the thoughts of Jerry, K.C. and others who have struggled with the 9mm accuracy problem.

My starting point is the famously accurate 38 Special 148gr HBWC round out of the really good PPC guns, which pretty much all seem to use barrel twists of 10-12".  The Remington Targetmaster 148gr round runs about 770 fps, and out of a barrel with 12" twist is spinning 46,200 rpm at the muzzle.  Since that round is so accurate, my thought is that the 147gr 9mm bullet, which is only .002" smaller in diameter than the 38, should also be accurate if spun at the same rate.  Unfortunately, to get the 147gr bullet up to that rotation using common 16" twist 9mm barrels requires a muzzle velocity of about 1026 fps, which is nearing a maximum load and certainly would not qualify as low recoil. Essentially, my thought is that if we had match quality 9mm barrels with a twist of 10-12", we could push something like the 147gr XTP at a speed of only 750-800 fps with the fast spin (46,000+rpm) needed for accuracy, and yet have a relatively soft recoil.  In fact the 147gr 9mm bullet and the 148gr 38 bullet pushed at the same speed would have essentially the same "calculated" recoil impulse.  I know the "felt recoil" would be different because the case capacities are different, but they would be close.

At the risk of damaging my own argument, I will note that I am aware that some of the most accurate 9mm ball guns are using the KKM 32" twist 9mm barrel and a 115 grain bullet.  Even at a blazing 1200 fps that barrel is only spinning the bullet 27,000 rpm, which I guess must be enough to stabilize that short bullet.  But frankly I am puzzled that the slow twist works so well on even the short 115gr bullet.

What do you 9mm 'smiths think?  Am I off track here?

I am new to BE shooting and am rejuvenating this old post in an effort to add some modern day input.

1. Is the 147gr 9mm in 1911 hardball gun the standard now?

2. As I read through the OP question and follow on comments, I can’t help thinking that 115gr shot slow but spun fast in a fast twist barrel could be a low recoil option also. The 115gr bullet could still be launched with the appropriate RPM but at lower velocity & lower recoil. Is there some reason that this will not work?

Thanks,

-Trevor