School me on twist rates

[historian]

So...1:8, 1:9, 1:7. In 5.56 does it really matter?

 

[OneBadV8]

depends on what you're trying to accomplish with the rifle. If you want to stretch it to 600 yds and use heavy bullets, it might.

If you want to shoot at classes or 100yds, it probably doesn't make a difference.

 

[ChristianPatriot]

depends on what you're trying to accomplish with the rifle. If you want to stretch it to 600 yds and use heavy bullets, it might.

If you want to shoot at classes or 100yds, it probably doesn't make a difference.

What he said. Here's a couple stability calculators if you're really curious

http://www.bergerbullets.com/twist-rate-calculator/

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

[wsenefeld]

Ever plan on shooting a 7.5" barrel suppressed?

 

[cavskillz]

View attachment 42116

 

[Leo]

I have bought or rebarreled every AR I have owned to 7.7 or 8 twist, with the exception of the COLT HBar that was 7 twist. I have never had one that had accuracy problems with any bullet 52 grains to 77 grains. All mine are rifle length, I have never played with pistol barrels in the .223 caliber.

 

[historian]

Ever plan on shooting a 7.5" barrel suppressed?

If I go SBR suppressed it will be a 300 BLK, so I'm probably just going to build a 5.56/.223 and then when I get some coin build a 300 blk with a SBR and a can. I figured I'd practice on the cheap stuff.

 

[throttletony]

these guys above have pretty much said it all. I might add that (1) bullet weight and (2) bullet design are both important.

Any of my varminting and target shooting (all within 300 yds, usually within 150) have been fine with 52, 53, 55, 62, and 70 gr bullets. I now have a 1:8 twist, but also used a 1:9 twist before.

They say that the dangers are on the extreme ends of the spectrum -- if you shoot a really light bullet with too much spin, it can potentially disintegrate and/or eat up its velocity with the overrotation. On the other hand, and heavy bullet from a slow twist will not stabilize and you'll be lobbing tumbling bullets at the target. Middle of the road on both bullet weight and twist rate usually leads to hassle free reliability. Your particular gun might prefer a certain loading, but reliability should be fine with any reputable ammo and gun manufacturer

For *MOST* people using the 223/5.56 within normal circumstances a 1:7, 1:8, or 1:9 should work fine.

Side note -- many old school and new school varminters like a 1:12 twist with light bullets (40-45 gr) to be able to crank up the speed. Before some of the modern bullet designs (v-max, etc), this was one of the best ways to get explosive impacts on little critters.

 

[natdscott]

In 5.56 does it really matter?

It matters in every rifle. Have you ever seen a rifle chambered in .244 Remington? No? It was twist rate that killed it, and even with the advent of the revised 6mm Remington, Ilion never could catch up with the rifles that were by then already rolling off a competitor's line in a cartridge you've probably known your whole life:

.243 Winchester.

Big Red got the barrels right the first time, even if they were later to the party.



So as has been said: what'cha gonna want the rifle to be able to do?

You have to get this barreling answer right the first time.

-Nate

 

[historian]

I am mainly thinking about a SHTF/Plinking rifle. Easier on the arm than the 91/30 and a whole lot lighter to, but still has centerfire power. Plus it is a building experiment, as this will be my first one.

 

[natdscott]

A NATO 1:7 Chromed barrel is the way for you.

-Nate

 

[Bfish]

The best answer for this is "it depends" I don't want to send you to poor information, but there are some good sources out there for you to read up on and decide for yourself based on your needs/uses. Heck there are even some good youtube videos on it. For the most part it's nothing to get caught up in.

 

[natdscott]

What, Bfish? No offense intended, but that post of yours didn't say a whole heck of a lot.

Citation of said "sources"?

Links to videos?


-Nate

 

[Bfish]

Well I mainly wanted to get the point across the point that it truly does depend... And also for the most part in how the majority of rifles are used it doesn't matter. But it truly does depend on how he intends to use it if he's concerned about twist rate and getting the most out of his rifle in that way.
I probably should have provided some sources but chose not to, sorry but I'll explain...

To start the OP only tells us he is building an AR in 223/556. He doesn't say what he wants to use it for. While I would say for the most part go 1:7 just because it's easy to get ahold of and out there; if he wants to build things for other purposes that may not be the best choice. See the sited article as to why. If all he is going to shoot are 55 grain ammo it doesn't really matter if he has a tighter twist rate. As I said it's not a whole lot to get caught up in for what most people get an AR for. I bet most 1:7 rifles usually fire 55grain ammo and not the heavier stuff where they really shine. So as I was saying it really all depends, and it depends on information we don't have from him... If he just researches a bit I truly think he will make the best choice for him instead of just letting us tell him what to do without knowing since it's important to him. If he's concerned about accuracy he may want to buy a nice barrel. He may want a stainless steel barrel, and he may want it to be melonite/ a nitrided barrel. A chrome barrel is known to be less accurate than a nitrided barrel due to the process of chroming and how hard a nitrided barrel is. Barrel life really is not any better either. Recently there has been much more nitriding due to these reasons. While this is true, and I'd be happy to buy a nitrided barrel my go to 556 rifle is chrome lined, my 300blk nitrided. Some times you can get into steel types too such as 4140, 4150 etc and that has nothing to do with how it's made. Other things such as if it's CMV, stainless, CHF, chrome lined or treated another way, if it's HP and MPI tested, the length of it as well as many other things. Twist rate becomes a bigger deal if you are shooting "far." There are just too many things that go into choosing the right barrel for you beyond twist rate. However it's also not a huge deal for what most needs are. I am not trying to down play the choice of a twist rate however. It can be very, very important to precision and accuracy both. It's also worth noting that velocity will also come in to play.. It all get in to how far down the rabbit hole do you want to go?

I chose to inform that their are good sources out there rather than provide what I think is a good source to him because he can then choose the source he feels most comfortable with as i'll get to. For example you may or may not want to take some advice off of arfcom or you might... You can for the most part also trust a respected publication like guns and ammo, so see the link below. It actually does a great job at showing barrel twist rates and their purposes. Which are to perform best with certain projectile weights. It's pretty good stuff. btw Monty LeClair who he references in the article is here in Indiana and creates fantastic products. Just a fun fact but the mk rifles that come out of there are ridiculous. When working up the right loads guys are getting 1000 yards with the 556 guns. Granted that loads are for that rifle only and beyond pushing it, however it doesn't make it any less impressive.
How to Pair Barrel Twist Rates with Bullets - Guns & Ammo

Think about what you will be shooting and what works for you. 1:7 or 1:9 will be fine and those seem to be common today. 1:7 most. Read the whole thing but the end of the article is below and is the good take away to have from it.

"Matching the rifling twist in your rifle or carbine to the appropriate ammunition won’t guarantee great accuracy, but it will ensure the bullet is properly stabilized in flight. On the other hand, using a bullet that’s too heavy for your barrel’s twist is a virtual promise of poor accuracy and ineffective terminal performance. If you’re struggling with the accuracy of your modern sporting rifle, be sure you’ve properly matched your ammunition to the barrel’s twist."


Next you can choose to watch some stuff off of youtube about it from someone you like... Several people have videos about it, I have provided a video by James Yeager and what he says is correct and I tend to fall in line with. However, not everyone loves James Yeager and they may want to watch a video by Tim over at MAC or Mike aka mrgunsngear, and the list goes on... I would like to say though that there is some super good information out there by mrgunsngear about barrels! It's worth watching his stuff!
[video=youtube;ndeET4A67Dk]https://www.youtube.com/watch?v=ndeET4A67Dk[/video]

 

[natdscott]

Good post. Not a bad video except that it isn't completely correct, or it was based ONLY around Carbines.


6.5 or 6.75" twist barrels are specifically for shooting 90 grainers, mostly at 800+ yards. Mostly ONLY for 20" rifles or longer.

7.0 twist barrels are good up to 80 grain lead-core VLD's, and the steel core NATO ammo is stable in them down to very low temperatures.

7.5 and 7.7" twist barrels are good up to 80 grain VLD's.

8.0" twist barrels are good up to 80 SMK and 82 Berger, but may be marginal with 80 VLD's.

9" twist is an odd thing, even though many Savremchester rifles were built with them...I'd not go there. Only will stabilize up to 69 SMK, as a general rule, and that can even be marginal. Basically, my opinion of the 9" twist is that it's not slow enough to be slow, but it's not fast enough to be good for a true "heavy" bullet.

12" twist is good for varmint bullets, and will be very accurate...

...as is the 14" twist, but you want to be VERY certain about going this slow. Good loads with even 52 grainers will HAMMER in fast twist barrels while the opposite is not true.


That's as far into the rabbit hole as I am going for a "shtf/plinking" rifle (hence my 7" Chrome NATO recommendation).

 

[Leo]

I have seen several methods of mathmatically finding a suitable twist rate, similar to the links the Christian Patriot posted. They are generally pretty good. I have made tomato stakes out of perfectly servicable 9 twist AR barrels because they would not shoot the 75/77 bullets very well.

I have a Mossberg MVP varminter with a 24 inch barrel. It is a 9 twist but shoots 77 grain Noslers and Sierras about the best of anything. I double checked the barrel twist with a rod. It IS definately 1 twist in 9 inches. Maybe the extra barrel length gives just enough extra velocity to raise the rpm's? I am at a loss as to why I had a couple of 9 twist rifles that would not stablize the 75/77 grain class of bullets but I have one that does excellent.

When spending the money for new, premium barrels, I am still going to stay with 7 to 8 twist. I am an experimenter, but not willing to spend $100's to test any theories.

 

[Lee S. Forsberg]

Check out The Greenhill formula in Hatcher's Notebook.

 

[natdscott]

...The Greenhill formula...

...has mostly been proven to be a little antiquated and less accurate way of calculating appropriate twist rates than is Miller. (caveat being that I certainly do not hold a degree in Physics)

For the lay person, JBM's calculators are probably the appropriate method. Used in a little more sophistication, and in conjunction with a spreadsheet, they will allow you to build a fairly accurate chart of what stability factors will be achieved across multiple sets of environmental parameters.

If anybody wants to be a student of it though, I still recommend you learn to do the calculations yourself, on real paper, with a real pencil.

That being said, as much calculation as you want to do, at the end of the day, unless your barrel manufacturer can deliver extremely precise and extremely accurate twist rates in the barrel you purchase, you can end up getting hosed anyway. This is one key differentiation between the barrels that "should" shoot (but don't), and the barrels that almost ALWAYS shoot. Choose carefully.

-Nate

 

[BOVindy]

I hate to thread hijack here, but nobody ever seems to mention minimum shootable bullet weight. I am looking to get something in the 1-6 to 1-8 in order to be able to shoot .224 bullets up to 82-83 grains. The rifle is a .223 A.I. What is never mentioned though, is that you might end up with a minimum bullet weight based on how fast your twist is. I was wondering if anyone would be able to tell me what the minimum bullet weight is for 1-6, 1-6.5, 1-7, 1-7.7, 1-8 twist barrels. Thank you for your time. -Ben

 

[natdscott]

There is no minimum, Ben. There MAY be minimum advisable weights for non-match grade loads, but really good ammunition made with light bullets will usually shoot pretty well through fast-twist rifles. A prime example of this is the fact that many VERY good shooters practice with 52/53 grain BR bullet loads in their 7-8" twist rifles otherwise dedicated to the consumption of 77-82 grain match LR loads. I'm talking TINY groups at 50-100 yards.

Now don't go so far as to think that 55 UMC ball or XM193 is going to shoot bugholes form your 7-twist...ain't gonna happen. But that's an ammo problem.

For your .223 AI, there is NO reason to go faster than a 7.7 Krieger unless you intend to shoot the 90-grain VLDs. 6.5's are dedicated, extremely specialized barrels for one thing: 700+ yards. 7.0" twist is fine, and accepted.

Do NOT try for a 6.0" twist. Ask Ms. Gallagher...it doesn't turn out well for bullets being able to make it to the target. I know of nobody with one.

Take that to the bank.

-Nate