need advice on twist rates for .223/5.56

[socalbeachbum]

what guidelines do you follow for twist rate in an AR-15 barrel? I shoot what is available which seems to range from 50 to 75 grain. 55gr is the most common.

I believe my Spike's Tactical 10.5" is 1 in 7 and my Lothar Walther 16" is 1 in 7".

At 1 in 7" what bullet weights should I use, theoretically?

 

[osprey176]

With a 1/7 twist,you can shoot pretty much any available bullet in a 5.56.I shoot heavy bullets in my 1/8 with no problems.

 

[joed]

People are going to tell you they shoot 45 gr bullets accurately with a 1:7 twist, I tend to not believe someone that says so. I use 75 gr bullets for mine, that's what that twist was designed for. My AR will shoot 55 gr bullets also but not with any accuracy like the 75 gr.

The rate of twist pretty much determines what projectile the gun shoots. Start using different bullets and accuracy does suffer.

 

[socalbeachbum]

so what is the rule of thumb? is it greater twist for heavier bullets?

if you have to choose, out of 1 in 9, 1 in 8, 1 in 7, what would be the best rate to choose for typical common 55gr ammo?

 

[R.W.Dale]

With the exclusion of very light varmint bullets coming apart due to centripetal force there is no such thing as overstabilization.

Get the fast twist. IMO slow twist 22 centerfires are obsolete

 

[R.W.Dale]

My AR will shoot 55 gr bullets also but not with any accuracy like the 75 gr.

er.

If by 55 g bullets you mean FMJ-BT it's not your twist rate. They just simply shoot like crap in any twist

 

[XD Fan]

I have a nice factory built AR with a 1:7 twist rate, but I have been looking at some inexpensive build kits just because I want to build one. Many of the less exspensive one seem to come in 1:9. Is there any correlation between costs and twist rates?

 

[HoosierQ]

I have a 1:9. I am sticking with 55 grains simply because currently I don't reload. At the 55 grain level I can get lots and lots of FMJ, some of it cheap. I can get really good varmint ammo. All of these are going to shoot to more or less the same point of impact, at about the same velocity. Thus I have effectively standardized on 55 and thus I hope not to have variation in my point of aim. You are going to get a lot of passionate and varied opinions on this subject.

 

[Theohazard]

With the exclusion of very light varmint bullets coming apart due to centripetal force there is no such thing as overstabilization.

That's simply untrue. Sure, an over-stabilized bullet is much better than an under-stabilized one, but an over-stabilized bullet tends to be less accurate than a properly-stabilized one, especially at longer ranges.

Here's an excellent sticky regarding .223 and 5.56 twist rates from another forum.


As you can see from the data, over-stabilized bullets tend to be a little less accurate than properly stabilized ones.

 

[4thPointOfContact]

Twist rate isn't really about bullet weight but rather about bullet length. The 1:7 was adopted to deal with the long, tracer bullets used with the M249 SAW (M196 - 54-grain and M856 tracer cartridge - 63.7-grain bullet).

In general...
1-in-14" - 55gr or less
1-in-12" - 35gr up to 55-60gr
1-in-9" - 45gr-75gr, possibly up to 77 if you're lucky
1-in-8", 1-in-7" - 45gr - 80+gr
NB.... Technically this should be about Length and not the Weight, but since most loads available are essentially copper clad lead cylinders instead of having a lightweight tracer compacted into a hollow base, going by weight is easier.

Given my druthers, I'd want as little stabilization as possible. Much better to have the bullet tumble upon impact than drill a nice, neat hole which is what is more likely to happen with over-stabilization.

 

[ugaarguy]

Much better to have the bullet tumble upon impact than drill a nice, neat hole which is what is more likely to happen with over-stabilization.

That's a myth. You cannot stabilize a bullet so much that it won't tumble when encountering a soft medium like flesh. Tumbling is affected by bullet shape, construction, and velocity.

 

[4thPointOfContact]

I stand corrected. In that case I'll take whatever combination of shape, construction, velocity and anything else that will promote the most violent tumbling out to the longest range.

 

[sarduy]

so what is the rule of thumb? is it greater twist for heavier bullets?

if you have to choose, out of 1 in 9, 1 in 8, 1 in 7, what would be the best rate to choose for typical common 55gr ammo?

i had that choice when i build my rifle and i wen't for a 1/7 twist, because it allow you to use anything from 45-75gr, and those people who tell you that you can't shoot 45gr bullets accurate enough, i invite them to shoot my AR anytime.

 

[Theohazard]

those people who tell you that you can't shoot 45gr bullets accurate enough

Nobody here has said that, all we said was that 45 gr. bullets will usually be more accurate in a slower twist like a 1:9 or a 1:12. A 1:7 is perfectly capable of shooting light bullets, but a slower twist will usually do it a little better, that's all.

 

[1911 guy]

I've been a fan of the 1:9 for a long time, but recently built a 1:7 M4gery. It stabilizes 55gr just fine. I did try some 50gr loads and they shot decently. I didn't try any 45gr, but i have some I might try next. However, I have heard many accounts of people who have tried the light bullets in a 1:7 and results are mixed. Some barrels seem to deal with them just fine, others not so much.

The old saw "Every rifle is a law unto itself" seems to be appropriate here.

 

[Infidel4life11]

All my factory AR's have 1:7 barrels just because it's milspec and I shoot 75-77gr bullets (Hornady 75gr tap and MK 262 77gr). I practice a lot with 55grs and have to change my zero down and right 2 clicks each.

Military uses 1:7 for no other reason than the use of tracer ammo.

I have a few rifles I've built using SS barrels with 5R rifling and 1:8 twist and they group better than any other AR I've owned or shot using the same 75-77gr bullets.

From my own shooting: I used my BCM 1:7 BFH 16" next to a friends Stag 1:9 16". I shot a 10rd group from each with 55gr pmc and 62gr M855. Same ammo lot # and all. With the 55gr the Stag grouped better that the BCM. With the 62gr the BCM grouped better. By better I mean 1/4"-3/8" tighter group.

It is what it is FWIW, I shoot 30k+ rounds a year (pistol&rifle) outside the Army and to be honest I would have been fine with a 1:9 twist and 55gr bullets for all my training purposes and any threat inside of 300m. If I knew the zombies were coming tomorrow and the position I'd be in I'd still want my fast twist and heavier bullets.

 

[tuj]

1:7 should like 75-77gr bullets. My 1:8 does a lot.

55gr bullets shoot ok in a 1:8 twist and I'd expect the same in a 1:7, just 'ok' results, nothing to take pictures of.

 

[gazpacho]

The Ammo Oracle is your friend.

This is a good bit of information about 223/5.56. I recommend it to everyone with questions on that subject

 

[Cee Zee]

They just simply shoot like crap in any twist

My 1:9 bolt .223 has shot 55 gr. bullets better than any other. It generally shoots 68-75 gr. stuff better but the best group I ever shot was with 55 gr. ammo. I have no problem with any ammo up to and including 75 gr. but above that I lose accuracy.

 

[IROCZ]

I'm presently building a couple 20 inch scoped rifles. I plan to use the 1x9 twist as I am more concerned with the longer range potential of the rifles. The 55gr. M193 type is still the most common round available in quanity but the quality is all over the place. The LC stuff seems to group very well.

 

[R.W.Dale]

my 1:9 bolt .223 has shot 55 gr. Bullets better than any other. It generally shoots 68-75 gr. Stuff better but the best group i ever shot was with 55 gr. Ammo. I have no problem with any ammo up to and including 75 gr. But above that i lose accuracy.

fmj bt?

 

[Robert]

My 1:7 barrel shoots 55gr OK, 69gr pretty good, and 77gr amazingly well.

 

[MistWolf]

A bullet cannot be over-stabilized. It's either stable, or it's not. If the bullet is spun so fast that it wobbles and hurts accuracy, it's not stable.

When choosing a bullet, the first concern is choosing the right type of bullet construction for the job. Second, is choosing the most accurate bullet of the construction type needed. The only way to determine if a bullet is accurate enough for the intended job is to shoot it.

RPM stabilizes bullets. RPM is the result of twist and velocity. You can have a fast twist, but if the velocity is too low, the RPMs will be too low to stabilize the bullet.

Bullet length and shape determines RPM needed for proper stabilization, not bullet weight. (There is also the fact that if you shove a bullet out fast enough, you can just about stabilize it with little to no twist at all. That's how the smoothbore cannon of the M1 Abrams works but that takes a lot of speed.)

Even so, every barrel is a law unto itself. Regardless of it's twist, you won't know what bullet it will shoot well until you actually shoot it

 

[Theohazard]

A bullet cannot be over-stabilized. It's either stable, or it's not. If the bullet is spun so fast that it wobbles and hurts accuracy, it's not stable.

OK, but usually when people say that a bullet can't be over-stablized, they're saying that you can't spin a bullet so fast that its accuracy suffers. They're saying that lightweight bullets are just as accurate out of a fast twist as they are out of a slower twist, and that's simply not true.

 

[MistWolf]

OK, but usually when people say that a bullet can't be over-stablized, they're saying that you can't spin a bullet so fast that its accuracy suffers. They're saying that lightweight bullets are just as accurate out of a fast twist as they are out of a slower twist, and that's simply not true.

When people say "over stabilized" to describe a bullet that's spinning so fast it hurts accuracy, they are incorrect and are causing confusion. The more stable the bullet, the more predictable it's flight path. In other words, the more stable the bullet, the more accurate it flies.

Bullet weight has little to nothing to do with how fast it must spin to be stable. It's bullet length and shape. The longer the bullet, the more RPM needed to stabilize it. "But a longer bullet is always heavier", you say. No, that's not true. A bullet made from less dense material to the same size and shape will be lighter. Bullet shape also affects bullet length. A .244" 100 gr VLD bullet will be longer than a .244" gr round nose and a round nosed bullet in general stabilizes at a lower RPM than sharply pointed bullets.

Some shooters report excellent accuracy with short bullet in tight twist barrels. You won't know if a short bullet will be less accurate in a tight twist barrel until you actually go out and shoot them. If it doesn't is it because the twist is too tight, or because the shorter bullet has to make a longer jump before engaging the rifling?