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 Rates of twist
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Pip
Junior Member

USA
224 Posts

Posted - June 04 2021 :  12:34:32 AM  Show Profile  Reply with Quote
Is it KNOWN what the currently desired/effective rate of twist is for 55gr. M193 in a 20" AR15M2 and 16" A4? So many rumors floating around
Thanks!
Pip

Frogfoot
Senior Member

USA
940 Posts

Posted - June 05 2021 :  6:35:41 PM  Show Profile  Reply with Quote
As far as I know, the twist rate for the M193 load was 1-12, but that was for the M16A1 rifle. Apparently, it was 1-14 for early M16 series rifles but they went to the 1-12 later on. The M16A2 variant used a fast 1-7 twist because of the length of the bullet used in the M856 tracer loading. I'm pretty sure the M16A4 used the 1-7 twist also as do the M4 series rifles. When I was in the military, we were taught that the M193 could be used in the 1-7 twist M16A2 rifle, but that the maximum effective range would be reduced because of the lighter bullet.

We make a living by what we get, we make a life by what we give. - Sir Winston Churchill
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Chris Christian
Advanced Member

USA
3878 Posts

Posted - June 06 2021 :  06:09:38 AM  Show Profile  Reply with Quote
My experience has been that a 1-9 twist seems to work well with every 5.56mm I've tried between 50 and 75 grains.

Chris Christian
There are those who make things happen. There are those who watch things happen. There are those who wonder What The Heck happened! Pick one.
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Jim Higginbotham
Moderator

USA
9957 Posts

Posted - January 28 2022 :  3:00:55 PM  Show Profile  Reply with Quote
quote:
Originally posted by Chris Christian

My experience has been that a 1-9 twist seems to work well with every 5.56mm I've tried between 50 and 75 grains.



That seems OK to me. I do own several 5.56 and .223 rifles in 7" twist as well and I have a gunsmith mounting a ne barrel on an old Model 70 that came with a 1 in 12 twist - the new barrel is 1 in 8"

But, as Chris says, in in 9 will usually handle 75. I've got some 80 gr bullets I want to try - they work fine in 1 in 7 and I'm hoping 1 in 8.

That is about as heavy as I want to go but I haver a friend who set a 1000 yard record - I think it was at a military base in Alabama (perfect score all Vs or Xs - I forget which) using 100 gr. .22s in a .223 (but he had to load them individually since they wouldn't fit in the magazine.

Jim H.

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WR Moore
Advanced Member

USA
1089 Posts

Posted - February 09 2022 :  8:45:49 PM  Show Profile  Reply with Quote
The American Rifleman did some comparative tests some time back and found 1-9 had the best accuracy for most bullets in common use at the time. 1-9 stabilizes the Hornady 75 gr HPBT, but not the A-Max, which is longer. We had 1-7 Colt HBARs and experienced some issues with 55 gr soft point bullets coming apart within 100 yards. Didn't happen until 20-30 rounds had gone down range. The ammo maker tested rifles and ammo and suggested use of a round with a thicker jacket.

Beware the politically obsessed. They are often bright and interesting, but they have something missing in their natures, there is a hole, an empty place and they use politics to fill it up. It leaves them somehow misshapen. Peggy Noonan


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gauchobill
Advanced Member

1212 Posts

Posted - February 10 2022 :  07:19:45 AM  Show Profile  Reply with Quote
Are there any studies of differences in twist rate in the wide variety of 9mm handguns? Any studies on differences in parabolic twists vs. the conventional cut rifling twists?
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WR Moore
Advanced Member

USA
1089 Posts

Posted - February 11 2022 :  10:33:29 AM  Show Profile  Reply with Quote
S&W apparently used 1-18.75 for anything remotely .35 caliber (and possibly some others, but I've lost my chart) for decades. They recently supposedly switched to the usual 1-10 for the M&P9 series. While some claim the 1-10 is superior because of the "higher torque reaction value" (of the bullet taking the rifling), I think that's angels dancing on pin heads territory. I really haven't seen any notable differences. But then I've never shot 147 gr bullets at BB gun velocities to just barely make minor caliber power factor.

If parabolic means polygonal, various sources indicate it can be bullet weight/length sensitive. If you're referring to 5R type rifling, I doubt any difference is going to show up at typical pistol ranges.

Beware the politically obsessed. They are often bright and interesting, but they have something missing in their natures, there is a hole, an empty place and they use politics to fill it up. It leaves them somehow misshapen. Peggy Noonan


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Chris Christian
Advanced Member

USA
3878 Posts

Posted - February 11 2022 :  1:08:11 PM  Show Profile  Reply with Quote
quote:
Originally posted by WR Moore

S&W apparently used 1-18.75 for anything remotely .35 caliber (and possibly some others, but I've lost my chart) for decades. They recently supposedly switched to the usual 1-10 for the M&P9 series. While some claim the 1-10 is superior because of the "higher torque reaction value" (of the bullet taking the rifling), I think that's angels dancing on pin heads territory. I really haven't seen any notable differences. But then I've never shot 147 gr bullets at BB gun velocities to just barely make minor caliber power factor.

If parabolic means polygonal, various sources indicate it can be bullet weight/length sensitive. If you're referring to 5R type rifling, I doubt any difference is going to show up at typical pistol ranges.



I use the 9mm a lot in competitive shooting. I've found the 1-10 twist works well for all bullet weights. I have a 1-16 twist barrel (which circumstances forced me to buy), and while it's as accurate as a 1-10 with 115 and 124 bullets, it sucks with 147.
Same is in rifles -- heavier bullets need a faster twist rate.

Chris Christian
There are those who make things happen. There are those who watch things happen. There are those who wonder What The Heck happened! Pick one.
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Ten Driver
Advanced Member

2062 Posts

Posted - February 12 2022 :  03:04:21 AM  Show Profile  Reply with Quote
S&W changed the twist rate in their M&P9 pistols after it was determined that the slow twist wasn’t properly stabilizing some types of duty ammo.

I won’t reveal the manufacturer, but they were getting complaints from some police agencies that their ammo wasn’t performing as advertised when tested in ballistic gelatin. This didn’t jive with the manufacturer’s experience, so the problem was analyzed, and it was discovered that the M&P pistols weren’t stabilizing the rounds, which were striking the gel at varying angles of yaw. A JHP bullet won’t expand properly if it hits sideways, instead of nose-on!

Once the twist rate was fixed, the bullets flew true and started working as advertised.
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WR Moore
Advanced Member

USA
1089 Posts

Posted - February 13 2022 :  7:34:23 PM  Show Profile  Reply with Quote
I have a 5906 I bought new back in the last century. It shot 147 gr Hydra-Shoks into one ragged hole at 25 yards. I say "shot" because the ammo was free and my eyes aren't what they used to be so I haven't tried it since. IIRC, velocity was something just north of 900 f/s. I kinda have to wonder about what was different with that specific ammo that had issues?

Added edit: it belatedly dawned upon me that if the bullets in question were lead free, the additional length might have caused instability with the 1-18.75 twist. I haven't tried monolithic copper bullets, but I have used rifle bullets with cores of atomized copper and some matrix. They're surprisingly long for weight. The 55 gr did stabilize in 1-9 twist 5.56 mm barrels.


Beware the politically obsessed. They are often bright and interesting, but they have something missing in their natures, there is a hole, an empty place and they use politics to fill it up. It leaves them somehow misshapen. Peggy Noonan



Edited by - WR Moore on February 15 2022 02:34:17 AM
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Evan
Administrator

34969 Posts

Posted - February 15 2022 :  1:41:39 PM  Show Profile  Reply with Quote
I like green tip and reports from a bud who shoot a bunch of people with it confirmed my choice!

"The greatest thing a Father can do for his children is to love their Mother."

Harold B. Lee

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