AR guys: 1:7" and 1:9"

[NWcityguy2]

Here is a question I have. Is there any reason you would buy an AR/upper with a 1:7 barrel over a 1:9 other than to shoot longer bullets?

I'll start off by saying I'm not an AR guy. I do shoot 3-gun though only 2-3 times a year. The reason I ask is because I see 1:7 becoming more and more popular and at lower price points than before. I also see almost everyone shooting bullets as long or shorter than SS109/XM855 which do fine in 1:9. I figured I'd ask to see if there is something I am missing.

(The one thing I'm not asking is which AR you wouldn't buy for some other reason. People can get emotionally invested in these guns and I understand that but it's just not what I am asking about.)

 

[MutinousDoug]

The 1:7 will wear faster than the 1:9 barrel regardless of what bullet length/weight you shoot in it due to the more rapid acceleration of rotation at the throat.

 

[benzy2]

There isn't much drawback with an AR shooting mid to upper weight bullets through a 1:7" barrel. You may blow the jackets off of the lighter varmint bullets if you push them hard through a 1:7" but mid to heavy weight bullets will shoot just fine. Some claim there is accuracy drop off in the middle (low to mid 50's gr) weight bullets through a 1:7" but others have shown quality barrels holding groups with these middle weight bullets that are under 1" at 100 yards.

A 1:9" twist will stabilize most anything you can load to mag length in an AR that isn't a tracer. If you don't plan to shoot at the outer ranges of the .223/5.56's capability you won't notice a difference in a 1:9" and a 1:7". Lots of high power shooters are shooting the mid to upper 70gr bullets that fit in a mag out of a 1:9" barrel with little to no ill effect. A few barrels struggle at this weight/length bullet with a 1:9" twist but I wonder if that is a quality control issue (being exactly 1:9" or slightly slower) as there are plenty of 1:9" barrels that will handle them.

If you plan to single feed the heaviest/longest bullets available you will need a faster twist than 1:9 and if you want to play with the mid to upper 70gr bullets that will seat to mag length you may want to bump to 1:8" just for the added peace of mind.

Personally, outside of the match shooter trying to launch the really long bullets I wouldn't let twist rate hold much value on the barrel I picked. I would look at manufacturer reputation first and barrel profile second (may switch those two in order depending on the rifle's purpose).

If I found a good barrel in 1:9" for a decent price I'd buy it.
If I found a good barrel in 1:8" for a decent price I'd buy it.
If I found a good barrel in 1:7" for a decent price I'd buy it.
If the barrel profile/manufacturer I wanted only offered the barrel I wanted in one of those twist rate options I'd buy what the offered and be fine with it.

I suppose though, in a perfect world, where all barrels were made of equal qualities, I'd buy the faster twist as I do like to play more with the longer bullets and have played with (and enjoyed) shooting the 75+ gr bullets from an AR, which some required the faster twist. I don't varmint hunt though and if that were a consideration I'd probably go with the slower twist just to add a few of the lighter options to the mix.

 

[cfullgraf]

The folks already posted have good information.

To add my take on it.

If you do not plan to shoot heavy bullets (>62-69 grains) the 1-9 twist barrel will work fine. Some 1-9 twist work with 69 grain or so bullets but you do ot know until you try.

If you want to shot light bullets (<50 grains or so), the 1-7 twist barrel may be too fast a twist.

I tend towards 1-7 twist barrels with my 223 Rem ARs and they work quite well with 55 grain bullets and up.

Hope this helps.

 

[benzy2]

Also, there is a lot more to do with barrel wear than twist rate. If you had two identical barrels of the same steel grade and manufacture process that varied only by twist rates and shot identical ammo through both, the faster twist would wear out faster. How much faster depends on many variables.

There is also the question of type of steel used, if the barrel is chrome lined or not, how well it was lined, if it was hammer forged or not, if it's given a nitride process/coating, what bullet weight is selected and how hard it's driven. I'd take a 1:7" twist barrel with one of the tougher alloys hammer forged with some of the better chrome lining shooting light varmint loads to last a lot longer than a 1:9" twist unlined barrel of one of the lessor alloys that was button rifled pushing the heavier bullets as hard as possible. While this is a bit of an exaggeration it's more to show that barrel life has to do with many factors beyond the simple comment that 1:7" twist barrels wear out faster. If all other factors are equal then yes, if not, it depends.

 

[minutemen1776]

I've had both, and I could tell no difference shooting 55- and 62-grain bullets. I shoot a 1:7 barrel now, but only because that's what was available with a chrome lining.

 

[Infidel4life11]

I usually look for a 1:7 Cold Hammer Forged chrome lined barrel. My AR's see a lot more rounds a year than most. If your weapon isn't going to be shot a lot (thousands of rounds a year/competition) and you are using cheaper store bought ammo then you don't need a 1:7 CHF CL barrel.

 

[OilyPablo]

My 1:7 DD barrel shoots 62gr bullets more accurately and repeatedly has tighter groups than 55 gr bullets. With 55 gr I get a tiny little scatter. Using my A.R.M.S. BUIS the 62gr bullets end up in a perfectly vertical line, varied only in height by where I line up(or down) the front sight with the blurred target bullseye. I've now shot nearly 1000 rounds of each, so it's not accidental.

 

[Ro1911]

I like 1 in 9 because I shoot cheap 55 grain all the time, 1 in 7 isnt as accurate with the cheap stuff.

 

[C-grunt]

I prefer a 1in7 as I like to shoot long distance with my Colt/ACOG combo every so often. The 75 and 77 grain bullets do better out of the faster twist barrels. My Colt still shoots cheap 55 grn ammo accurate enough to be a threat out to 500 yards or so.

Also at work many of the Bushmasters, 1in9 barrels, keyhole our frangible training ammo that we use in the shoot house. The Colts, 1in7 barrel, doesnt. My duty gun will keyhole on a target as close as 10 yards or so with that ammo.

 

[Caliper_Mi]

75 and 77gr bullets are becoming more common and both can be loaded to mag length. If you desire to do longer range shooting, the heavy bullets will resist the wind better and need 1:7 or 1:8 twist to stabilize for sure. If you're only shooting 62gs bullets, 1:9 is fine.

 

[gotigers]

For competition, i like 1:8. I shoot a lot of 55gr at targets within 50 yards in 3 gun, but i will sometimes shoot 68-75gr for longer shots if there is wind. My 18" FA/Criterion barrel 1:8 shoots Hornady steel match like a dream, sub MOA.

For a plinker, i prefer 1:9.

If i were only shooting 55-62gr, i would stick with 1:9. However, i agree with benzy2, i would buy 1:9,8 or 7 without pause if i liked the AR.

 

[JustinJ]

The 1 in 9 on my AUG shoots 75 grain better than anything else i've put in it and i've tried quite a bit of "match" ammo of all weights.

 

[NeuseRvrRat]

the long and skinny of it is few casual shooters actually need the 7" twist, but it's popular because that's what the M4 has.

 

[benzy2]

JustinJ, your experience matches mine. The 75gr and 77gr bullets that fit in a magazine tend to shoot just fine out of most 1:9" twist barrels. The longer Hornady 75 gr Amax bullet, which won't fit a magazine, won't stabilize in many/any 1:9" barrels I've seen, but again it is a single load affair. The Hornady 75gr Match bullet along with the SMK 77gr bullets have both shot fine out of my 1:9" barrels along with many other people. These both happen to seat to proper length to feed from a magazine as well.

 

[joed]

I'll give you my take on it.

Four months ago I was looking at AR's. I noticed the Colts had a 1-7 twist while most others had a 1-9 twist.

At one time I owned a Savage bolt action with 1-9 twist that shot 69 gr bullets great but anything 75 gr or more was iffy at best.

So, I bought the Colt AR with 1-7 twist. It was May when I bought the Colt. Here we are in August and I'm seeing the companies that were 1-9 starting to change over to 1-7.

I think you're going to see 1-7 become popular with the use of 75 gr or heavier bullets. And I hope I don't see the day ofa 1-4 twist shooting 200 gr bullets.

 

[mortablunt]

I think it's to do with accuracy at range. 1:9 will not stabilize the heaver, bigger bullets as well as a 1:7 would. In just shooting for fun, it's a moot point. In competition and purpose builds, it does matter.

 

[ATLDave]

I have a Sig 556 (not known as the most accurate rifle) with a 1:7 twist barrel. For whatever reason, there is a noticeable accuracy difference between bullet weights. It's not accurate at all with 55's, does better with 62's, and significantly better with 69's and 70's. Of course, the latter tend to be "match" bullets anyway. Just one more data point for you to consider.

 

[mtrmn]

The Colt 20" HBARs that were used before the M4 had 1/9. I have one. It shoots 69gr SMKs just fine.
The M4 uses 1/7 simply because of the much longer tracer rounds. The longer the bullet, the faster twist you need. The tracers wouldn't reliably stabilize with 1/9.
Most any bullet you want to use from 50 grains on up will be fine with 1/7, and I would not hesitate to buy either twist.
That said, most of the hype ("I'd never buy a 1/9, etc") about the 1/7 is just that, hype. It stems from those who worship the mil-spec chart, and anything that's not exactly like the chart says is blasphemy in their eyes. I agree if my life is going to depend on my gun, I want it as tried and true as possible, but the rifling twist rate makes no difference to me or the bad guy downrange as long as it's reasonably accurate. I stay within my accepted range of 50 - 70 grain bullets and have no problems whatsoever.

 

[gotboostvr]

I went 1 in 8 and it makes me look like I know what I'm doing behind the trigger regardless of bullet weight.

I'm in the planning stages of a lightweight carbine/HD AR with a long list of specif features I'm looking for and barrel twist isn't on it.

 

[ugaarguy]

The Colt 20" HBARs that were used before the M4 had 1/9. I have one. It shoots 69gr SMKs just fine.
The M4 uses 1/7 simply because of the much longer tracer rounds. The longer the bullet, the faster twist you need. The tracers wouldn't reliably stabilize with 1/9.

Not quite. Very early experimental M16s had 1:14 twist barrels, The M16 as adopted for general issue had a 1:12 twist, the M16A1 retained the 1:12 twist. The M16A2 went straight to 1:7 twist before the M4 even existed. 1:9 twist barrels, and heavy barrels of any twist, have never been standard issue on the M16 rifles.

That said, most of the hype ("I'd never buy a 1/9, etc") about the 1/7 is just that, hype. It stems from those who worship the mil-spec chart, and anything that's not exactly like the chart says is blasphemy in their eyes.

Not really. The faster twist is needed to stabilize longer projectiles. In conventional copper jacketed, lead core construction bullets right at 70 grains (give or take one or two grains) is the maximum most 1:9 twist barrels will stabilize.

Many folks also fail to understand that alternate construction bullets may be shorter for their weight (PRL / DRT powdered tungsten-tin core, uncommon), or longer for their weight (Barnes, Hornady, etc, copper solids, very common).

It's that last bit, those copper solids, that we really need to pay attention to. All ammunition containing lead is banned from hunting use in California. Many ranges have been forced to go lead free to meet EPA and / or lower level government requirements. Beyond those factors, Barnes did a great a job with their marketing and made copper solids mainstream by showing the mainstream shooting community how tough the solid copper construction is. Copper solids are a reality that isn't going away.

Here's the crux of the issue. The 55gr Barnes MPG needs a minimum 1:9 twist to stabilize. Step up to a 62gr TTSX and 1:8 twist is the minimum to stabilize.

Considering that: 1) a 1:7 twist bbl will shoot US M193 (55gr lead core FMJ) just as accurately as a 1:12 twist barrel of equal quality (as documented US Army FM 23-9), 2) a 1:8 twist or faster is required to stabilize most conventional lead core bullets over 70 grains, and 3) a 1:8 twist or faster is required to stabilize most copper solids over 60 grains; a 1:7 twist bbl on an AR just makes more sense than a 1:9 twist.

 

[helotaxi]

the faster twist would wear out faster.

Within the .223 pressure range this won't hold true. Barrels don't wear out form the projectiles going down them. Imparting spin on a bullet does nothing for wear. The throat of the barrel wears because of heat, pressure and powder burning in that part of the barrel. If it weren't for the powder combustion, a barrel would last essentially forever.

As far as a slower twist barrel shooting lighter bullets better, unless you are shooting bullets that should have been culls in the first place (in which case you're talking about a bullet that patterns rather than groups from any barrel anyway) you will not notice the difference with an AR between the 1:9 and 1:7 with any bullet that the 1:9 will stabilize. You might find a 1:7 that shoots light bullets poorly, but that will be more a case of the load and barrel combination being a poor match than the rate of twist being the problem. Shoot a quality bullet through a quality barrel with a rate of twist adequate to stabilize the bullet and you will get good accuracy as the rule. Certain barrels not liking certain bullets becomes the exception.

As far as what rate of twist is needed for your application, a quality barrel that is indeed a 1:9 will shoot pretty much anything that will fit in the magazine. That includes the 62gn TTSX Barnes bullet. Barnes recommends a 1:8 but the Miller index for that bullet at 2700fps on a cool day at sea level is a 1.12 which is stable. Getting warmer or higher increases that number. The real problem that you run into with those bullets is that they intrude on a lot of powder space and the heel of the bullet is well below the shoulder/neck junction on the case which isn't the best scenario for efficiency or accuracy.

Too many people make way too big a deal about rate of twist in ARs. If you don't reload or shoot expensive long range match loads that don't fit in the magazine, you will be well served with a 1:9. Focus more on the quality of the barrel. I've seen many more high quality (with regard to accuracy) barrels with a 1:9 or a 1:8 twist than a 1:7. I've had excellent results with Hornady match HPBT 75gn bullets from my quality 1:9 barrels. If the barrel that you want, from a quality perspective, is a 1:9 buy it. 99% of shooters will never have an issue. The 1% that will understand why they need something different an are spending a lot of money on a match grade barrel and will be spending a lot of money on match grade (and very long) bullets.

 

[drsfmd]

So, I bought the Colt AR with 1-7 twist. It was May when I bought the Colt. Here we are in August and I'm seeing the companies that were 1-9 starting to change over to 1-7.

Citation please? To the best of my knowledge, there's no major manufacturer who has changed from 1:9 to 1:7 in the last four months. There's no minor manufacturer that I'm aware of making that change either.

The manufacturers who are making 1:7 have all been doing so for a while.

 

[carbine85]

I don't get hung-up on the 1:7 twist. It was built for the military to shoot longer heavier bullets so therefore everyone had to have one. The fact is for most of the 55 -62 grain ammo that you buy the 1:9 is a better choice. For target shooting the 1:8 is the best choice. Most AR target shooters use the 69 gr bullet and it matches up nicely with the 1:8. That's why almost all stainless heavy match barrels are 1:8. At least that's the way it is around here.

 

[helotaxi]

The 1:8 comfortably gets you into the 80gn lead core bullets like the Sierra MatchKing or the Hornady Amax. 1:9 is fine with 69gn and as I said earlier mine shoot the 75gn hpbt very well. I haven't tried the 75gn Amax but it is a very long bullet for it weight so I'm not holding out a lot of hope on that one. The reason that most of the match shooters use a 1:8 is that is what most match barrels are cut with. It allows up to 80gn bullets but most matches don't require shooting to a range where they offer an advantage and the won't feed from a standard mag.

Look at what blanks are available at what quality, material and price point. Stainless match barrel blanks are typically cut with high power and service rifle use in mind and 1:8 has become the standard for that discipline for the reasons touched on above. with the advent of the 90gn SMK and the Berger VLDs in that discipline 1:7 match barrel blanks are becoming more common. In the world of hammer forged, chrome lined barrels most of those barrels are made on the same machines that make M16/M4 barrels and as such they are 1:7 by default because that is what is specified by the DoD. The DoD went to a spec 1:7 specifically because of the 64gn tracer round in combination with Arctic conditions. It is overkill for that purpose even, but that was the design goal.