1:9 Barrel Twist and Ammo

[a59cheffy]

Sorry if this has been discussed before, searched and couldn't find relevant posts...

I was told by the gun rep's at Bass Pro Shop that the 1:9 barrels (5.56 M&P2) like a heavier bullet, 65 to 75 grain. All that I have read tells me otherwise. I am certainly not going to shoot competition but I would like to match ammo weight to distance and accuracy.

What ammo is this rifle most "comfortable" with in the 100-200 yard range?

 

[Westie1]

When it comes to "salespeople" at bps, a lot of them know less about guns then my wife. And she's not a shooter-yet.

With the 1:9 twist that the Sport II has, you're looking at bullets in the 50-65gr weight range. Some 68/69 gr loads may work. How well a specific load will work is dependent on what your barrel likes. For general range use, any of the common 55gr loads will work.

If you're looking for the best accuracy, then it becomes a matter of trial and error to see what your particular barrel likes. And that's where things like a good scope, improved trigger, and reloading come into play.

 

[andy52]

My 1:9 shoots a 65 gr very well, above that it will stabilize the heavier bullets but doesn't shoot them accurately. If you reload try the Sierra 65 gr gameking with a lot of trial and error that the one mine likes best.

 

[C J]

I have a bolt action .223 that has a 1:9 twist that shoots 75 gr. ammo very well. It's the best weight for that rifle. But it has a much longer barrel than my AR's. And that makes a difference.

 

[Hunter991]

Actually what they told you is incorrect. 55-65 gr is generally what shoots better in a 1:9 twist. Doesn't mean your Sport won't shoot heavier bullets but as a general rule they are incorrect.

 

[hdrolling]

1:7 twist 55-85 gr
1:8 twist 50-80
1:9 twist 45-74

 

[wayne2356]

Found this a long time ago ...

Common AR-15 rates of twist vary between 1:7 and 1:12, but why should you care what your rate of twist is, right? The reason is because different bullet weights perform better with certain rates of twist. So if you are just going to go plinking and do short- to medium-range target shooting, you may be happy with 40 grain bullet weights, which would mean a 1:12 rate of twist would be ideal for you.
If you are shooting long range, or want more penetration, you want a heavier bullet in the AR, such as a 62- or preferably a 77-grain. 62-grain bullets prefer a rate of twist around 1:8 and 77-grain bullets weights favor a 1:7 twist rate.
All of this being said, these days finding ANY AR-15 ammo is almost like winning the lottery, and if you are lucky enough to find any at all it is likely going to be the most common bullet weight which is 55-grain (a 1:9 twist rate). Ideal rates of twist for a particular bullet weight are somewhat subjective; however opinions will not vary greatly among the experts.

Bullet Weight: The Ideal Rate of Twist
So to simplify this for you, here is a chart you may want to print:

Bullet Weight Twist
40-Grain 1:12
55-Grain 1:9
62-Grain 1:8 or 1:7
77-Grain 1:7 or 1:8
80-Grain 1:7
As you can see from the chart, the heavier the bullet you want to shoot, the faster the rate of twist should be to most effectively stabilize the bullet. It’s not that you can’t shoot AR ammo that is on one end of the spectrum through a barrel with a twist rate at the other end of the spectrum, it’s just not ideal. You won’t get maximum effectiveness of your ammunition. One thing that can happen is over-stabilization; this occurs when you shoot a bullet through a barrel with too fast of a rate of twist for that particular bullet weight.
Here’s an example: you shoot a 40-grain AR bullet through a barrel with a 1:7 rate of twist; the bullet will over-stabilize and this will make the bullet not fly completely true at longer ranges. But you wouldn’t want to shoot a light AR bullet at long ranges anyway.


So what’s the best all-around rate of twist?
The M16A2 comes with a 1:7, and the military typically shoots bullet weights from 52 grains up to 77 grains, with 62 grains being the most common in combat. Most experts would agree that the best all-around rate of twist would be something in the middle such as a 1:8 or 1:9. I personally like the 1:7 or 1:8 rate of twist because I like to shoot long range in the desert. A downside to this is that it is generally believed that the faster rate of twist means the faster you wear out your barrel. That being said, you should ask yourself what kind of shooting you envision yourself doing and pick a rate of twist accordingly.
Lastly, most manufacturers do not offer different rate of twist options within a particular AR model. Typically, each model line is going to have a given rate of twist and that’s it.
So you should know what your intention is with your prospective new AR purchase beforehand, and select a model that has a barrel with a rate of twist that is consistent with your primary goals for the rifle.

 

[hdrolling]

The main reason the military uses 1:7 is to be able to shoot tracer rounds.

 

[vonn]

I have .223/5.56 in 7,8,9,and12 twist rates and don't see much difference for most of my uses. I do my best to figure out what a particular rifle likes and that is what I go with. They are all acceptably accurate with cheap 55 grain for plinking and would do ok in pucker situations. One hole shooters go to extreme measures to make one hole but it can be done if you have the dedication.

 

[rockquarry]

Try several weights / bullet designs."Suggested" means just that: what usually works best. It's not an absolute rule. You might also measure the twist rate of several barrels. It's not a rare occurrence to find some variance.

 

[Shooter Mike]

I had the same question for my new CZ 527 in .223 with a 1:9 twist
so I called Hornady and talked to a customer rep.

I shoot paper and I wanted their opinion for the most accurate ammo that they make for my set up. He recommended 68gr. BTHO Match ammo, item number 80289.

I am a newbie as well but I managed to shoot 1" groups with this ammo out to 100 yds. This week I will move back to 150 yds.

I hope this helps.

 

[agksimon]

Here's a chart that reflects general consensus.

 

[hugger-4641]

At 200 yds or less, you're not going to notice that much difference in groups size of bullet weights, given the same quality of ammo. Now, if you try to compare Hornady Black with Tullamo, you are going notice. I have a Sport II with a 1/9 and abother Ar with a 1/7. They both shoot anything well out to about 200yds, but past that , the heavier bullets like the 1/7 .

 

[hdwhit]

Here's a discussion of twist rate and bullet weight for 223/5.56 from Stag Arms, an AR manufacturer. You can not only see the twist/weight pairings others have given without citing to a source, but you can read the rationale behind it.

How Barrel Twist Rate Affects Ammunition Choice

And echoing what others have said, anything the guy behind the bun counter at a big box store tells you is only going to serendipitously be correct. In my experience, you would often be best served by doing the opposite of whatever they recommend.

This goes all the way from the guy who refused to sell me a rifle when I was 19 because he "knew" you had to be 21 to buy a rifle right up to the guy who told me I had to buy the Ruger AR556 rather than the Smith & Wesson Sport II because the Ruger had a chrome lined barrel.

 

[hdwhit]

What ammo is this rifle most "comfortable" with in the 100-200 yard range?

At 100 to 200 yards, a 1:9 barrel is likely to be "comfortable" with anything you shoot out of it.

First, it needs to be understood that twist rates actually have nothing to do with bullet weight. They have to do with bullet length. If you are shooting a conventional gilding metal jacketed lead core bullet of a particular diameter, then a longer bullet is going to weigh more, so bullet weights are often used as a proxy for length, but when you start to add hybrid, composite and lower-weight metals like solid cooper to the discussion, the distinction becomes relevant. Thus, if you are shooting a 60 grain solid copper bullet, you will need a 1:7 twist rate because the bullet will be very long even though with a lead bullet, you could probably have gotten away with a 1:12 twist.

Second, faster twist rates become more important as the distance increases because the cumulative effects of the disturbances in flight the engineers call "pertrubations" start to accumulate the longer the bullet is in the air and the slower it rotates as it slows down in response to air resistance. At 100 to 200 yards, even a long bullet is still traveling fast enough (and rotating fast enough) the perturbations have had less time to act, so twist rate is not as significant.

 

[C J]

Second, faster twist rates become more important as the distance increases

I don't doubt what you say is true but it's also true that heavier rounds are less affected by wind at longer distances. I have a bolt action rifle that will shoot a 75 gr bullet 500 yards and hold a 5" group most of the time. Wind becomes more of a factor with lighter bullets from what I've experienced. On a windless day I've actually shot better groups with 55 gr bullets but on a day with wind the heavier bullets do better.

 

[a59cheffy]

Thank you all, knew I would get a quick education from ya'll !! Been shooting 62 grain fmj Federals at my outdoor range with irons. And was completely surprised at the accuracy with my old eyes at 100 yards. Just an amazingly designed rifle...

 

[hugger-4641]

If you are pleased with those Federals, you will really be happy when you try some better quality ammo or good re-loads.

 

[WR Moore]

At 100 to 200 yards, a 1:9 barrel is likely to be "comfortable" with anything you shoot out of it.

First, it needs to be understood that twist rates actually have nothing to do with bullet weight. They have to do with bullet length. ..... but when you start to add hybrid, composite and lower-weight metals like solid cooper to the discussion, the distinction becomes relevant. Thus, if you are shooting a 60 grain solid copper bullet, you will need a 1:7 twist rate because the bullet will be very long even though with a lead bullet, you could probably have gotten away with a 1:12 twist.

Ah, NO! It's a combination of weight AND length. 1-9 was found to be most accurate of all the twists for bullets in the middle of the weight distribution in testing by the NRA.

I've seen proper stabilization of the 75 gr Hornaday HPBT match bullet in 1-9 and the Barnes RRLP 55 gr bullet that's well over an inch long due to the copper powder matrix core. This was out of both 16 and 26 inch barrels in both cases.

Hornaday does advise that 1-9 will not stabilize their longer 75 gr A-Max bullets. I proved that 1-10 won't stabilize the 75 gr HPBT, the bullet goes through a target sideways at 25 yards. That twist does shoot the 69 gr SMK outstandingly.

 

[SRT]

As a general rule of thumb, projectiles that are shorter/lighter need a slower twist, while longer/heavier require a faster twist rate.

At the end of the day, however, the only real way to tell if your particular rifle likes a specific bullet is to try it. After more than 50 years with the AR platform, I have found that there are no shortcuts. You have to get out and shoot with a good rest to see what the rifle does.