ChattanoogaPhil
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1:7 vs 1:8 vs 1:9 rifling twist rate
- Thread starter Rastoff
- Start date
My exposure to high power rifles has been mostly directed to target rifles. Back when I was whole, I started with an M1903A3NM, graduated to an M1MkII, then an AR. I managed to earn my NRA XTC Master classification with the AR. My AR service rifle is a post ban Colt Match Target A2 with a 1:7 twist. I would shoot magazine length 77gr SMK out to the 300 yard line. At the 600 yard line, I preferred 80gr SMK loaded singly. I was told to expect a target accuracy life of about 5000 rounds.
After my accident, I built a 1:8 twist Frankengun AR with the intention of shooting 1000 yard F class. That is still a work in progress.
Over the course of about 25 years and numerous discussions in the pits at Perry, the concensus has been that for service rifle competition, either a 1:7 or 1:8 barrel is a necessity in order to be competitive at the 600 yard line. For me, a 1:9 barrel just can't be competitive beyond the 300 yard line.
This summer, I am looking at adding a twist to my shooting. Having been a right handed shooter all my life, I am looking to shooting my AR match rifle and service rifle left handed, because I need to get back on the game I have grown up with.
After my accident, I built a 1:8 twist Frankengun AR with the intention of shooting 1000 yard F class. That is still a work in progress.
Over the course of about 25 years and numerous discussions in the pits at Perry, the concensus has been that for service rifle competition, either a 1:7 or 1:8 barrel is a necessity in order to be competitive at the 600 yard line. For me, a 1:9 barrel just can't be competitive beyond the 300 yard line.
This summer, I am looking at adding a twist to my shooting. Having been a right handed shooter all my life, I am looking to shooting my AR match rifle and service rifle left handed, because I need to get back on the game I have grown up with.
ExcitableBoy
US Veteran
For me, an AR is an AR is an AR. I've owned a number of them from Colt, Ruger, etc. (The Sterling AR-180 doesn't count, but in my mind it was a much superior rifle.) The only AR-15 platform I have now is a cheapo ATI Omni Hybrid with a 1:7 twist rate. I don't expect it to be an MOA bullseye rifle, and it isn't. Just as I don't expect it to last forever, unlike my expectations for my hand-built Marlin-Ballard .22 lr Schuetzen rifle.
Though I've nailed my share of deer with an AR, I have long since relegated them to varmint control, both four- and two-legged varieties. The Omni came in quite useful about 4 hrs. ago when I spotted a big ol' raccoon staggering (obviously diseased with who-knows-what) down my fence line. I don't even recall offhand what loads are in it right now, but I flipped on the reflex optic, set on the finest green dot, popped it off safe and planted one in it's neck at 75 yards.
The raccoon didn't care what the twist rate of the barrel was, nor the bullet weight or it's composition. And I guess I don't much care, either. It did what it was supposed to do with decent accuracy, and that's all I can ask of it.
Now, that Marlin-Ballard, and my bolt guns... well, they're an entirely different story.
Though I've nailed my share of deer with an AR, I have long since relegated them to varmint control, both four- and two-legged varieties. The Omni came in quite useful about 4 hrs. ago when I spotted a big ol' raccoon staggering (obviously diseased with who-knows-what) down my fence line. I don't even recall offhand what loads are in it right now, but I flipped on the reflex optic, set on the finest green dot, popped it off safe and planted one in it's neck at 75 yards.
The raccoon didn't care what the twist rate of the barrel was, nor the bullet weight or it's composition. And I guess I don't much care, either. It did what it was supposed to do with decent accuracy, and that's all I can ask of it.
Now, that Marlin-Ballard, and my bolt guns... well, they're an entirely different story.
Jim Watson
Member
I went 'round and 'round with that notion.
I really got sucked in and put on a 6.5 twist for 90 grain bullets.
Theoretically, it should shoot like a 175 gr .308 but in practice it does not.
And the pit crew hates looking for the small holes.
At midrange, it is a different story, it is a FINE 600 yard rifle.
I now think your 8 twist and a fast 75-82 gr is the better approach at making a Long Range .223. So does Eric Stecker.
hdwhit
Member
It depends.
- The grade of steel the barrel is made out of will affect longevity.
- Chrome plating or surface nitriding versus nothing at all can impact longevity.
- What the jacket of the bullet is made out of can affect longevity.
- How fast you fire (and the resulting heat of the barrel) can affect longevity.
This is a link to a "torture test" in which rifles were intentionally abused to see what impact some of these factors would have on the life of the barrel.
http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/
Note that although the article is captioned as a comparison of brass versus steel "case" ammunition, the effect of gilding metal jacketed bullets versus bi-metal bullets are also addressed.
In this abusive situation the barrels firing the bi-metal bullets were shot out by around 6,000 rounds while the barrel shooting the gilding metal bullets was still servicable after 10,000 rounds. I would think that gently used barrels would last at least that long.
This is the closest thing I've seen to proof regarding this issue. Did you see for yourself that a 1:9 wasn't competitive at 600 yards? Sometimes consensus is wrong but usually not especially at Perry.
FWIW I have a 1:9 .223 varmint rifle. It will shoot a 5" group at 500 yards consistently with my best group at that distance being 1". But it's not an AR obviously. It has a 26" barrel. I shoot 75 gr bullets (Sierra boat tail in Black Hills Remanufactured Ammo cartridges). They are pretty consistent for off the shelf ammo. So it is possible for a 1:9 twist to shoot well but again it isn't a service rifle.
Brian in Oregon
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I want maximum accuracy from 55 grainers, so 1:9" is the fastest twist I'll accept. I rarely shoot anything heavier.
It really boils down to what bullet weight you will primarily shoot, or whether you want to cover all bases with maximum twist rate with a degradation in accuracy for lighter weights at longer ranges.
If all you are doing is shooting tin cans and zombie targets at 50 yards, it doesn't matter one iota.
It really boils down to what bullet weight you will primarily shoot, or whether you want to cover all bases with maximum twist rate with a degradation in accuracy for lighter weights at longer ranges.
If all you are doing is shooting tin cans and zombie targets at 50 yards, it doesn't matter one iota.
Most standard ARs that are sub MOA shooters are in the hands of the Internet.
It's a whole lot easier to shoot sub-MOA groups on a keyboard-assuming we're talking about multiple shot groups-than it is on a range.
hugger-4641
Member
My 2 Cents
IMHO, unless you are competition shooter or you are trying to drive tacks at 400yds, you are not going to notice any difference between a 1/9 and a 1/7 twist. Here's a pic I took this weekend. I was shooting 55gr Tullammo thru my 1-7 twist barrel at 220 yards using a cheap Tasco Red Dot. That is a 9" diameter paper plate I used for a target, held by tacks at top and bottom, but for some reason the pic posted sideways. I couldn't do any better using the 1-9 twist barrel with the same ammo, and couldn't do any better with the 75gr BTHP Hornady Black that I shot also. When I get a good scope, I might be able to improve, but for now, at the distances I'm shooting, I can't see any difference between the 1-7 and 1-9.
IMHO, unless you are competition shooter or you are trying to drive tacks at 400yds, you are not going to notice any difference between a 1/9 and a 1/7 twist. Here's a pic I took this weekend. I was shooting 55gr Tullammo thru my 1-7 twist barrel at 220 yards using a cheap Tasco Red Dot. That is a 9" diameter paper plate I used for a target, held by tacks at top and bottom, but for some reason the pic posted sideways. I couldn't do any better using the 1-9 twist barrel with the same ammo, and couldn't do any better with the 75gr BTHP Hornady Black that I shot also. When I get a good scope, I might be able to improve, but for now, at the distances I'm shooting, I can't see any difference between the 1-7 and 1-9.
Moe Mentum
Member
I only shoot 55 grain bullets, so 1:9 for me.
