AR 15 Twist

[quedz]

[Mindless-Focus]

Yup. I keep this on my phone. I prefer 1:7.

[Dolomite_supafly]

Funny, my 12 twist barrel is the most accurate barrel I have ever shot and it shoots 62 grain bullets the best. 12 twist will shoot everything from 62 grain on down and do it better than any of the other twists. Last time I had it out I was shooting 62 grain bullets and they were hovering right around an inch at 100 yards. If I shot 10 then 6 of them would be inside of an inch and the rest would bring the group to 1.5".

 

If accuracy concerns you then you want the slowest twist you can get that will stabilize the bullet you are most likely to shoot. For me the bullets I will shoot the most are 55 and 62 grain so for me a 12 twist is perfect. If SHTF today and I felt I needed to carry an AR it would be my 12 twist gun.

 

It is more accurate than my 9 or 7 twist barrels but you can see one side of the bullet hole isn't as sharp as the other side. All this means is the second they hit an organic target the bullets will tumble and hopefully fragment. My 12 twist shoots MOA using handloads using 62g M855 bullets while the others do not shoot as well. My SHTF AR has a 20" barrel so velocity is high enough that the bullets should fragment inside of 200 yards but even if they don't the bullet will still tumble causing damage.

 

An 8 twist barrel will shoot EVERYTHING that will feed from a magazine. 9 twist will shoot everything up to about 77 grains but all barrels are slightly different so verify before shooting through a silencer. With a 7 twist you are limiting yourself to ~50 grain, or heavier, bullets. Yes, you can shoot lighter bullets but some will sling the jackets right off the bullet with the faster twists. And there really is no need to use a 7 twist unless you are shooting 80+ grain bullets but once you get to about 80 they rounds can no longer be fed from a magazine and must be loaded one at a time.

 

8 twist is the best compromise between them all. The best way to figure out what twist you need is figure out which bullet you are most likely to be shooting and use the slowest twist that will stabilize it. In this case a 12 twist will be the best with 55 grain bullets but because you might also be shooting some heavier stuff or at longer distances I would go with a 9 twist. A 9 twist will let you shoot the most common stuff as well as the heavier stuff without the bullet being too stable. And this will ensure the bullets will tumble when hitting an "organic pop up target".

 

The wounding mechanism for FMJ bullets is tumbling and then fragmenting. First the bullet must tumble then, if the velocity is high enough, the bullet will fragment. Now if you have a twist that is too fast for the bullet then the bullet will not tumble, at least not inside the target, and in turn the bullet will not fragment. But if the twist is slow enough the bullet will first tumble inside the target and then the bullet will fragment providing the velocity is at least 2,500 fps. But it might require more or less velocity depending on the thickness of the jacket. Now even if the bullet is not going fast enough to fragment it should still tumble. If you shoot 55 grain bullets out of a 7 twist it is possible for the bullet to not tumble and pass through the target without doing a lot of damage like a 22 lr. This is why we are hearing all the reports of the 5.56 being ineffective against the thin middle eastern men. The way to fix that is to either go with a slower twist or a heavier bullet.

 

And the problem is not with the caliber as long as you realize it is a short range cartridge. It worked great until the bean counters decided having a 7 twist would be better for shooting tracers. Then after that the government decided to try to make this short range cartridge into a long range cartridge which, as we have heard, did not do so well. If they really wanted to fix the problems with a 5.56 they would accept the fact it is a short range caliber and either use a much heavier bullet or a much slower twist. As it stands right now the military is using the worst of all worlds, a twist that is too fast, a barrel that is too short and a bullet that is too light for the twist.

 

In the end if I had to choose one twist for everything I might do it would be a 9 twist barrel. It is still slow enough that most bullets will readily tumble yet fast enough to stabilize most of the heavier bullets you might find.

 

Here is a pretty good read on what is going on overseas with the M855 and the faster twist barrels.

http://stevespages.com/pdf/5_56mm_military_info.pdf

[jpx2rk]

what length barrel is the graphic for?

[Dolomite_supafly]

what length barrel is the graphic for?

Twist have nothing to do with barrel length.

 

I hear people say a bullet must make one revolution in the barrel but that is complete an utter BS. If that was the case then no pistol would ever stabilize a bullet.

[Mindless-Focus]

The 1:7 in my 7.5 pistol in .223 Wylde is probably the most accurate pistol build I have in AR form. I love that build. It's a 1" group at 50.

[Caster]

Twist have nothing to do with barrel length.

 

I hear people say a bullet must make one revolution in the barrel but that is complete an utter BS. If that was the case then no pistol would ever stabilize a bullet.

 

 

 

Absolutely right.  Anyone who argues that point needs to spend time with muzzle loader shooters.  I've seen muzzle loaders clover leaf at a hundred yards running a 42 inch barrel with a 1/48 inch twist.  

 

It ALL about matching ALL of the components.  Building a "Do-All" rifle or trying to compromise and then being disappointed with the results is down right silly.  

[gregintenn]

Methinks too much credence has been granted to the almighty twist rate. I have ars with 1:7, 1:8, and 1:9 barrels. Unless you get into super light or super heavy bullets, I can't tell any difference. They are all super accurate with quality loads. Buy a quality barrel and be done with it.

To get more technical, bullet length is what actually affects stabilization as it relates to speed and twist rate rather than bullet weight. Edited April 27, 2016 by gregintenn

[Dolomite_supafly]

Something I have personally noticed between a lot of 5.56 guns. The faster the twist for a given bullet length the bigger the groups. Quality ammunition helps but you get more gains by matching your twist to the bullet.

 

It is not hard to see evidence either. Look at benchrest shooters. A lot of them are using 30 caliber bullets in their guns. Most are running lightweight bullets, like 110 or 125 grain. And with those bullets they are running twists that are 15, 16, 17 or even 18 and are shooting very, very tiny groups. If twist was not important they would be running a 10 or 11 twist.

 

So I pick a bullet weight for a given gun then I match the gun's barrel to the bullet's length.

[Omega]

Something I have personally noticed between a lot of 5.56 guns. The faster the twist for a given bullet length the bigger the groups. Quality ammunition helps but you get more gains by matching your twist to the bullet.

 

It is not hard to see evidence either. Look at benchrest shooters. A lot of them are using 30 caliber bullets in their guns. Most are running lightweight bullets, like 110 or 125 grain. And with those bullets they are running twists that are 15, 16, 17 or even 18 and are shooting very, very tiny groups. If twist was not important they would be running a 10 or 11 twist.

 

So I pick a bullet weight for a given gun then I match the gun's barrel to the bullet's length.

That would work once you get a good load worked up for said rifle, but I mostly stick with 1:7 or 1:8 so it can shoot varied weight bullets on my ARs.  I don't shoot bench so keeping it within a 4" circle is fine for any weapon I may use as an SD weapon.  On my hunting rifles (270 & .308) I try and stick with about 150 grain bullets and they have a 1:12 (I think), the new .277 WLV barrel came with 1:11 and heard it does well with up to 120 grain pills.  I have not yet started making rifle specific loads though, even for my 300BLK I reload for both the 10.5" (1:7) and 16" (1:7) using the same load.  Maybe if I started some long distance shooting or benchrest shooting I would change my methods but haven't got the itch for that yet.

[Dolomite_supafly]

I used to chase groups but I was spending more time doing prep than actually shooting. I guess I had an epiphany and just have up on it. But there are still a few things I do to all my brass regardless of its intended use. Debur and uniform the flash holes is something I will always do to my rifle brass.

[Omega]

I used to chase groups but I was spending more time doing prep than actually shooting. I guess I had an epiphany and just have up on it. But there are still a few things I do to all my brass regardless of its intended use. Debur and uniform the flash holes is something I will always do to my rifle brass.

I do pay extra attention to my hunting rounds, I figure the game is worth the effort. 

[Dolomite_supafly]

Hunting rounds require a lot more attention to detail than target ammunition. It is such an awesome responsibility to take an animal quickly and humanely. So hunting ammunition must not only be accurate but it must also be reliable.

[gregintenn]

I used to chase groups but I was spending more time doing prep than actually shooting. I guess I had an epiphany and just have up on it. But there are still a few things I do to all my brass regardless of its intended use. Debur and uniform the flash holes is something I will always do to my rifle brass.

I've never touched a flash hole. Do you really see any gain with this? If so, I'll get a tool.

[Dolomite_supafly]

Making sure the flash hole is uniform and chamfering the flash hole resulted in the single biggest improvement in groups sizes. It also helped my SD numbers get into single digits.

 

It was a culmination of a bunch of things but factory ammunition would hover around 3/4" and my worked over hand loads consistently shot .3's with enough .2's to know they were not a fluke either. But the biggest jump came from me working on the flash holes.

 

And here is the thing about doing flash holes. Yes they add some time but you never have to do them again. Do it at the beginning and you never have to touch them again.

 

If your flash hole has a burr and it forces the spark above the powder charge you will inconsistent ignition and velocity. When you chamfer them the spark will be the same every time you pull the trigger. Or if the flash holes are different sizes it can do the same thing. This results in random velocity changes as well as when the bullets exits the barrel during its whip.

 

I would sort bullets first by weight then I would sort them by bearing surface length. Bearing surface length can have a significant impact on velocity. The longer the bearing surface the more pressure and the higher the velocity. The shorter bearing surface will have reduced velocity. That causes vertical stringing. I would buy bullets in 500 round lots and would end up with 4-5 different lots. I would shoot up one lot then rework the load data with a new lot until it shot well.

[Urse]

Hmmm deburr my flash hole.........just sounds wrong :stare:

[musicman]

The real question is... how did you get a burr in your flash-hole to start with?!

[Omega]

The real question is... how did you get a burr in your flash-hole to start with?!

Bad maintenance, not enough lube? 

[Dolomite_supafly]

The real question is... how did you get a burr in your flash-hole to start with?!

 

The flash holes in the brass are punched out. And just like the 2000 election anytime you punch anything sometimes there is a little "chaff" left behind. And even if the chaff is not left behind the flash hole is often not ideal. So we use a tool to uniform the flash hole as well as chamfer it.

[mikegideon]

Making sure the flash hole is uniform and chamfering the flash hole resulted in the single biggest improvement in groups sizes. It also helped my SD numbers get into single digits.

 

It was a culmination of a bunch of things but factory ammunition would hover around 3/4" and my worked over hand loads consistently shot .3's with enough .2's to know they were not a fluke either. But the biggest jump came from me working on the flash holes.

 

And here is the thing about doing flash holes. Yes they add some time but you never have to do them again. Do it at the beginning and you never have to touch them again.

 

If your flash hole has a burr and it forces the spark above the powder charge you will inconsistent ignition and velocity. When you chamfer them the spark will be the same every time you pull the trigger. Or if the flash holes are different sizes it can do the same thing. This results in random velocity changes as well as when the bullets exits the barrel during its whip.

 

I would sort bullets first by weight then I would sort them by bearing surface length. Bearing surface length can have a significant impact on velocity. The longer the bearing surface the more pressure and the higher the velocity. The shorter bearing surface will have reduced velocity. That causes vertical stringing. I would buy bullets in 500 round lots and would end up with 4-5 different lots. I would shoot up one lot then rework the load data with a new lot until it shot well.

 

It depends on brass quality too. I have a tool for flash holes. But, if you use Lapua brass, you don't have to worry about it. In fact, you don't even have to size it out of the box the first time. So, if going for high accuracy, I just shoot Lapua brass. If going for "good" accuracy, I'll shoot something else. Kinda eliminates the need for a flash hole tool for me.

[Dolomite_supafly]

Lapua brass is great brass but you will pay a lot more than the cost of a fixing cheap brass with a $15 tool.

[mikegideon]

Lapua brass is great brass but you will pay a lot more than the cost of a fixing cheap brass with a $15 tool.

 

I don't buy it for the flash holes. I buy it for uniform neck thickness and things like that. But, I also don't buy it to shoot up close.

[gregintenn]

It depends on brass quality too. I have a tool for flash holes. But, if you use Lapua brass, you don't have to worry about it. In fact, you don't even have to size it out of the box the first time. So, if going for high accuracy, I just shoot Lapua brass. If going for "good" accuracy, I'll shoot something else. Kinda eliminates the need for a flash hole tool for me.

I use "a bucket of brass", unless I'm shooting for tiny groups. I have some Remington brass set aside for that.

 

Lapua is out of my price range for brass I'll be hunting for on the ground. In fact, Lapua is out of my price range period.

[Dolomite_supafly]

I have shot .3's using prepped Winchester brass. But I won't do that any more. I was spending way too much of my shooting time preparing to shoot. By the time I went through everything I bet I had 5 minutes in each loaded round. I quit doing most of the prep but still do the flash holes.