1:7 vs 1:8 vs 1:9 rifling twist rate

[Rastoff]

We haven't jumped down this rabbit hole in a while...

The 1:7, 1:8 and 1:9 rifling twist rates are the most common among modern ARs. All three are available on current model M&P15s.

I'm sure this has been discussed ad nauseam on many forums, but has a consensus been reached? Is one better than another? Is one more accurate? One more reliable? Does one last longer? Do you care?

 

[alexfitch225]

All of my barrels I get from armalite since they're close to me are 1:7, they seem just as good as my friends stag with a 1:8. Both are just as accurate, chalk me up for the I don't care category.
(Edit) I've also never shot out a barrel on a 1:7 twist.. and I'm talking I've beat the daylights out of my first m15 to the point where if the barrel were to be ***** it wouldn't surprise me at all but alas she keeps spitting rounds on target accurately.

Sent from my SM-G930V using Tapatalk

 

[jagular]

I'm sure this has been discussed ad nauseam on many forums, but has a consensus been reached? Is one better than another? Is one more accurate? One more reliable? Does one last longer? Do you care?

There will never be a consensus which is why you see all three still in production. In the end it depends on what type of round you want to use for your intended purpose.

 

[Westie1]

All depends on the bullet. Slower the twist, the lighter the bullet. More on twists etc here.

[ame]https://www.youtube.com/watch?v=R3FDLiWMUTc[/ame]

 

[sgtsandman]

I can't really add to this. It depends on what bullet weights you want to shoot as to what barrel would be best and even then; not all barrels, even of the same make and model, are created equally. What one rifle likes best, the next rifle of the same exact make and model and all other things being the same, may not like it.

In some ways, it like the pistol caliber debate. I don't think there will even be an agreement.

 

[apollo99]

Generally speaking 1:9 good for 55 grain 1:8 55-62 grain 1:7 62 grain and up. That's not to say you can't shoot any grain out of any twist barrel, but there is an optimal twist for a given bullet weight for stabilization. I'm giving a very simplistic version of this.

 

[hdwhit]

Rastoff wrote:
Do you care?

Not really.

For the vast majority of shooters it won't make a difference.

My 1:12 Mini-14 stabilizes 60 grain bullets out to 200 yards just as well as my 1:9 M&P-15 and I don't shoot anything heavier.

As to durability, simple physics will tell you that the stress of imparting a faster rotation (i.e. smaller number in the twist ratio) is going to cause greater wear than imparting a slower rotation. This would be accelerated using bi-metal rather than gilding metal jacketed bullets, but, this will be meaningless to most owners since they will never use the rifle enough to shoot out the barrel.

 

[Whitwabit]

I can't really add to this. It depends on what bullet weights you want to shoot as to what barrel would be best and even then; not all barrels, even of the same make and model, are created equally. What one rifle likes best, the next rifle of the same exact make and model and all other things being the same, may not like it.

In some ways, it like the pistol caliber debate. I don't think there will even be an agreement.

I looked at different ammo in different twist rates and basically found it all up to the individual rifle barrel on a particular AR ..

Like you said what one likes another may not even if set up the identical way .. and a bullet weight that isn't suppose to be as accurate in the twist rate on yours may well out shoot other weights ..

Can any one explain why ??

 

[Westie1]

No expert, but would hazard a guess that barrel harmonics has to play a factor. Since the barrel vibrates, if the bullet exits the barrel at the same point in the vibration every time, you'll get tight groups.

 

[WR Moore]

Several years back, the NRA did comparative tests with multiple firearms. The 1-9 twist won the accuracy test with all except the long, heavy bullets like the 77 gr SMK. The twist won't stabilize that load (or the 75 gr Hornaday plastic tipped bullet).

Yes, the bullet has to be both long & heavy. I've loaded some 55 gr Barnes RRLP bullets that are 55 gr and over 1 inch long. They stabilize just fine at 2920 f/s from a 1-9 16 inch barrel.

I've got a 1-10 barrel that will shoot 69 gr SMKs very well, 75 gr Hornaday HPBT keyhole at very close range. On the other hand, the 1-9 shoots the Hornaday bullet extremely well.

I can buy the theory that the faster twist leads to faster barrel wear, I'm just not sure most folks will ever fire enough ammo fast enough to really see a difference. If you're into multi mag dumps on a regular basis, maybe.

So, if you have some need-real or perceived- to shoot 77 gr SMKs (forget the military coding for the load) or similar loads, get the 1-7 or 1-8. Or, if you just gotta be mil-spec.

 

[Rastoff]

Lots of talk about longevity. How long should a barrel last?

I have over 3K through one rifle and it still shoots sub MOA. How long can I expect it to last?

 

[Dad_Roman]

Why you wanna make us put our "thinkin caps" on over the weekend???

Do you care?

Nope...

...thanks for askin though

How long should a barrel last?

10K+.....vids on YT of guys killin them on purpose just to answer this question. Check em out



Hope your havin as great a weekend as I...

 

[Jim Watson]

Generally speaking 1:9 good for 55 grain 1:8 55-62 grain 1:7 62 grain and up. That's not to say you can't shoot any grain out of any twist barrel, but there is an optimal twist for a given bullet weight for stabilization. I'm giving a very simplistic version of this.

I always wonder why the Internet tends to generate grossly overspinning bullets, especially in .223.

A 55 grain flatbase spitzer has been stabilized by a 14 twist with excellent accuracy for several decades now, certainly the 1958 .222 Magnum the .223 is based on and no doubt a bunch of earlier wildcats.
The Pentagon found a 12 twist needed for the 55 grain boattail in cold air.

The 62 grain SS109 partial steel core bullet does just fine in a 9 twist, as do some 75 grain lead core bullets.

The only thing in general use that demands the fast fast fast 7 twist of the M16 and M4 is the very long tracer bullet.

Target shooters debate over the advantages of the 7.5, 7.7, and 8 twists for their 75-82 grain boattails.


Barrel life depends on what you are calling "life." Shoot at tin cans and foreigners at moderate range... 10000 rounds. Shoot for X count at 600 yards, maybe 4000. Shoot for the small X ring of the F class target, maybe 2500.

 

[Jim Watson]

Generally speaking 1:9 good for 55 grain 1:8 55-62 grain 1:7 62 grain and up. That's not to say you can't shoot any grain out of any twist barrel, but there is an optimal twist for a given bullet weight for stabilization. I'm giving a very simplistic version of this.

I always wonder why the Internet tends to generate grossly overspinning bullets, especially in .223.

A 55 grain flatbase spitzer has been stabilized by a 14 twist with excellent accuracy for several decades now, certainly the 1958 .222 Magnum the .223 is based on and no doubt a bunch of earlier wildcats.
The Pentagon found a 12 twist needed for the 55 grain boattail in cold air.

 

[Jim Watson]

With the "recent improvements" why can I still not edit a post?

 

[Dad_Roman]

..................

 

[C J]

Any comparisons done should take into account all variables like harmonics, barrel length, etc. etc.. The list of variables is going to be long. And then there are the intangibles that we would all love to learn how to fix. One barrel made on the same line as another barrel may perform differently. Good quality control keeps that sort of thing to a minimum but it's still there even on the best barrels.

Absent any hard data on this question I don't see how we can draw a conclusion. As someone else said different tests have produced different results. This is a tough question really. There isn't a whole lot of difference in these twist rates. But some things have become accepted as consensus like the idea that it takes a faster twist rate to stabilize anything over 75 gr and that includes most 75 gr bullets too.

So until someone produces a comprehensive study (the kind the gun makers don't like to do because they keep people from doing their own experiments which means more money for them) I will grab my popcorn and take a seat and keep my 2 cents.

 

[Disabled1]

To me, it doesn't matter. I will only shoot 55 gr. ammo anyway (Unless there is an extremely insane low price on other weight rounds).
Now, if I HAD to choose a twist, I would choose 1:7 twist.

 

[ChattanoogaPhil]

I have two carbines. Both chrome, 1-9 and 1-7 twist.

They both shoot about the same with 55/62gr. I'll never be shooting 45gr but maybe 77gr though I doubt it. So I suppose if I had to pick one I'd chose 1-7, but for my current use twist rate don't matter to me. I'm not a precision paper puncher. Mostly shoot offhand at steel. Really, about the only time I shoot at paper is to zero an optic. With M855 and M193 they're both about 2-3moa shooters when I do use paper which is about what to expect from the ammo. Eh... whatever.

 

[Triathloncoach]

Does it make much difference in a normal factory M&P? Yes, they are accurate rifles in the right hands. Certainly not my hands. But these aren't meant to be precision rifles.