AR-15 Talk AR-15 General Interest

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Old 09-20-2008, 19:16   #1
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Twist rate, nato 1:7, compared to 1:9

Why is it that the NATO M16a2 has a 1:7 twist yet most commercial AR variants have 1:9.
Why not make them milspec on a 1:7 twist?
And 1:7 is difficult to find. Ive got a colt post ban HBAR with 1:7.
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Old 09-21-2008, 17:33   #2
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1/7 will stabalize a lot heavier of a bullet than most 1/9 will. A lot of 1/9 will lose it at the 65 range (a lot that won't too, but more ofthen than not), a 1/7 is good up into the 80's.
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Old 09-22-2008, 06:10   #3
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CMMG makes alot of 1/7 twist barrels. Their products are hard to get. Even if they are in stock it takes a month plus for them to pack it up and ship it. Their products are superior, their service is the opposite of superior. That entire logistics and the accounting/order taking operation needs to be outsourced.

Bushamster sometimes has them. I want a 14.5 heavy 1/7 chrome lined as a spare MG barrel. They havent been offered in a while. 11.5 Inch barrels still come in heavy and 1/7 though.

You may want to try Noveske. Ive heard they are nothing but the best thing in the AR barrel market. The N4 upper is a thing to have.
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Old 09-22-2008, 06:24   #4
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But why do most of the uppers sold today come in 1:9 instead of 1:7, thats what I would like to know?
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Old 09-22-2008, 12:37   #5
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Maybe because a 1/9 would stabalize a 55gr(I'm guessing the most commonly sold, walmart, etc. ammo) and lower more effectively than a 1/7 twist? Just guessing here.
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Old 09-22-2008, 17:31   #6
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The 1/9 twist gives the end user a better range of bullet choices. It should shoot bullets 45-75 grains with any luck. Some will, some won't. Barrel quality, Bullet velocity, and bullet shape will all affect the barrels performance.
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Old 10-09-2008, 12:57   #7
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i have 3 .223's 2 AR's and a mini all with 1:9 i think its a better twist that 1:7 because my personal stock pile is all 55, 62, 64, and some 69 gr bullets
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Old 10-09-2008, 14:47   #8
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Hi Rich,

The M16 family of weapons were fitted with 1:7 twist barrels in the early 1980s in order to stabilize the new composite core M855 5.56x45mm NATO ammunition, which was being adopted, along with the M249 SAW, at that time for US forces. Existing M16A1 rifles used a 1:12 twist rate for the rifling in their barrels, which was acceptable for stabilizing the then current M193 55-gr lead cored FMJBT round. M855 bullets have a center of mass further back on the round and this makes them more susceptible to tumbling in flight without a fast spin rate provided by barrels with tighter twist rates. As such the current M16A1 could not fire an M855 round for more than 100 yards or so without the onset of tumbling. I’m not sure the reasons why a 1:7 twist rate in particular was selected; there has been some speculation that this twist rate is a bit excessive for the M855 round. It is also possible that it provides extra gyroscopic stability for the use of other types of composite cored ammunition, existing or planned, such as the military M995 armor piercing round, etc.

So why do commercial AR15 clone manufacturers use a 1:9 twist barrel in their products? With the incredible rise in popularity of the AR-15 among civilian gun owners in the 1990s and 2000s, particularly post 9/13/2004, there existed a need for their products to fire a wide variety of ammunition with good accuracy. Commercial .223 Remington ammunition runs a wide gamut of bullet types, lengths, masses and configurations, so AR gunmakers building complete general purpose AR clones needed a rifling twist rate that would fire a jacketed, lead cored .224 bullet between 45 grains and 75 grains well. For this reason, a 1:9 twist rate works well because it will not overspin lighter bullets but can provide enough gyroscopic stability for the heavier 65-75 grain commercial ammo and thus it is used in virtually all civilian ARs. I personally prefer the 1:8 twist ratio myself, as it produces a bit better accuracy with the heavier and longer bullets.

Some manufacturers (Rock River, etc.) do offer the option of different twist rates for their rifles and these can also be sometimes custom ordered form the manufacturer. Colt used to sell all of their ARs with 1:7 twist and still do offer that rifling for their LE6920 rifles, which are the closest a civilian can get to owning an actual M4 carbine. The bottom line is that 1:9 twist is perfectly acceptable for regular target shooting and self defense with an AR, I prefer the 1:8 and the 1:7 is the current Mil-Spec
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Old 10-09-2008, 20:26   #9
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Thanks Fanatic! I thought you dissapeared from this board a long time ago. Glad to see you still hang out here.

Im fully aware of the history of the M16, especially through the development and Vietnam, Ive read quite a bit,and talked to many vets, but havent read so much past the early 80s.

The M16a2s that we have in the armory and the M4s that we have are all labled 5.56 Nato 1:7.

I grasp the concept of the civilian market using 1:9 for a good median for 55 to 75 grain ammo, but I guess, what Im really getting at, what puzzles me, is how they can label the barrels Nato 1:9, since that is not what we use in the military, hence it is not true "Milspec" and not Nato.

Therefore I beleive that marketing them as Nato 1:9 is false advertising.

I took my Colt 1:7 A2 20inch out to the desert a couple weeks ago. I was shooting 55gr soft point. It shot well, I wasnt shooting paper, just cans and skeet set up on a hill. 200-300yds no problem, so I know that ammo wont fly apart from being to light for the twist rate.
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Old 10-09-2008, 22:14   #10
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Hi Rich,

Yeah I left for a little while but have returned again.

The "NATO 1:9" barrel stamp is false. It's designed to appeal to the uninformed on that matter and those who buy AR-15s because they want to see what looks like an M-16 rifle sitting in their closet or gunsafe. I've said it before and I'll say it again: Unless you own a Class III M-16A4, built to MIL-SPEC MIL-R-63997 and applicable revisions by FN-HERSTAL at their factory in South Carolina, you do not own a current true MIL-SPEC rifle. Period.

Sometimes manufacturers will claim that their rifles or parts are "MIL-SPEC" because they do the required materials selection, or heat-treating or hard anodizing, etc. according to the MILSPEC listed above, but it still doesn't count. You either conform to the entire MILSPEC to qualify or it's not. There's no in-between.

The problem with firing a lighter bullet down a barrel with a fast twist rate isn't that the bullet will fly apart, it's that it's more resistant to following its parabolic flight path along it's longitudinal axis. It's similar to the problem of throwing a football with a lot of spin to it versus with just the right amount of spin to it. The properly thrown football will naturally follow its flight path whereas an overspun football will remain fixed in a particular orientation in space during its flight. I don't know if they still have it up but Fulton armory used to have a good dissertation on the physics of bullet flight on their website. You might snoop around that site and see if you can find it there.
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Old 10-10-2008, 08:51   #11
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Thanks guys, I consider myself a gun tech. junky, and even I had been sold the bill of goods that 1:9 was NATO spec! You even read it in the gun rags when they review ARs, I wish more companies were actualy marketing their barrels for legit NATO spec self deffense use, but unfortunately most manufacturers market to plinkers and varmit hunters who NEVER use anything over 55gr bullets. I've been wanting to shoot 70gr bullets through my AR, but as stated earlier anything over 65gr 1:9 civilian barrels don't like. I shot great groups with 55gr Win. boattials @ 100yds, couldn't even hit the target with Wolf 62gr @ 50yds.
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