1:8 or 1:9...

Wizbang

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1:8 or 1:9 twist in a 5.56 AR... if you need more info i can provide it i just dont know much about this stuff so thats why im asking hopeing to learn... thanks
 

RyanG

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I personally like the 1:8... it allows me to shoot the larger grain bullets and will still shoot 55 grainers as well. If you plan on shooting any kind of distance you will really want the faster twist rate so you can stabilize them. I shot a shoot last weekend and made the mistake of shooting 55 grainers. They worked very well out to about 550 when there was little to no wind. Next year I will be shooting the heavier bullets.

Hope that helps a little

Ryan
 

Kevin Thomas

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Wizbang,

The 1x9"s are really something of a hold-over, whose time has come and gone, at least in my opinion. The 1x9"s are ideal for 68-69 grain bullets, but won't handle any of the later developments like the 75s, 77s or 80s. The 1x7" or 1x8" will, and will also shoot the 69s just as well. A bit of extra spin will almost never cause problems, while insufficient spin is ALWAYS a problem. Go with the faster twists, and forget about the 1x9".
 

ICANHITHIMMAN

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Wizbang,

The 1x9"s are really something of a hold-over, whose time has come and gone, at least in my opinion. The 1x9"s are ideal for 68-69 grain bullets, but won't handle any of the later developments like the 75s, 77s or 80s. The 1x7" or 1x8" will, and will also shoot the 69s just as well. A bit of extra spin will almost never cause problems, while insufficient spin is ALWAYS a problem. Go with the faster twists, and forget about the 1x9".
Do this its good advice, I have a 1-7 in all of mine but the mil moved to a 1-8 for all its 18" barreled SPRs everything else is a 1-7. I think the 1-8 choice for the spr had to do with the bullets they chose to use. The 77g SMK (77g Nosler for a short time) etc. The magority of the guys have the 1-7 and are using bullets ranging from 62 to 77g.
 

Herzo

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Unfortunately, all of my AR's are 1:9, but they do handle the 69 gr SMK's very well. Berger has a 73 grain target that is supposed to be 1:9 friendly. Beyond those weights you start to run into problems with the magazine length.
 

Kevin Thomas

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The problems beyond these with the 1x9" remains one of twist, not mag length. So long as it's got a 7 caliber ogive or less, it will work as "mag length" at 2.260" The problem with the 75s-77s is that they need the faster 1x8" twist. I routinely use 77s for my Across the Course shooting, switching to 80s or 82s for the 600 yard stages, Since the 600 yard stage is designated as "slow fire", the rounds must be single loaded; the rules don't allow them to be fed from the mag. As a result, the heavier bullets intended for these strings generally use a 12-15 caliber ogive, and are usually seated out to around 2.450" or more. Here, the inability to function trhough a mag isn't a problem at all, and is what allowed the more extreme designs to come to be.
 

ICANHITHIMMAN

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I like the 1-7 in my 16" MRP a 70g ttsx fly's to the same point of impact as a 55g M885 at 100M. I only see myself going 1-8 or 1-9 if I was building a rifle for dog towns and wanted the real light explosive screamers. For what I do the 1-7 is perfect it allows me to use the 55g bullets for my inside 200m training and the heavy 70g bullet for the crop damage deer and what ever else in the summer.
 

rdsii64

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I am of the opinion that 1:8 is the perfect twist rate for a 223/556 AR15. That twist rate will work with EVERYTHING that will feed from an AR magazine.

My RRA Predator Pursuit rifle has a 1:8 twist. It will easily shoot inside the company's 3/4 moa accuracy guarantee with every bullet I have shot from the 40 grain varmint bullets to the 77 grain match bullets. In fact it works so well, I'm looking to re-barrel my bolt action 223 with an 8 twist barrel.
 

J E Custom

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The 1;9 will work in the 223 AI because of the increase in velocity especally with the heaver bullets

But for a strait 223/556 I would recomend the 1;8 twist for all bullets.

If you are going to shoot only the very large bullets then the 1;7 might be a better choice.

I rechambered a 223 in 1;8 to a 223 AI and it shoots under 1/10 th of an inch MOA.

The 1;9 is the preferred twist for the 45 to 55 grain bullets only.

J E CUSTOM
 

Lefty7mmstw

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moa here with hornady and priv. partizan 75 grain bullets in a 9" twist dpms with factory peeps. I agree that the 8" twist is better for the heavier pills, but I've shot hundreds of 75-77 grain out of a 9" twist with no accuracy issues. They are all bullets that can be loaded to mag. length and aren't the tipped or long ogive pills
 

rdsii64

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moa here with hornady and priv. partizan 75 grain bullets in a 9" twist dpms with factory peeps. I agree that the 8" twist is better for the heavier pills, but I've shot hundreds of 75-77 grain out of a 9" twist with no accuracy issues. They are all bullets that can be loaded to mag. length and aren't the tipped or long ogive pills
when it comes to shooting 77/75 grain bullets in a 9 twist barrel, its hit or miss. A true 9 twist barrel won't work with a 75/77 grain bullets. the catch is that many barrels that are marked as 9 twist barrels are actually 8.5 twist barrels. thats why you hear conflicting stories about 75/77 class bullets in a 9 twist barrel.
 

Lefty7mmstw

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when it comes to shooting 77/75 grain bullets in a 9 twist barrel, its hit or miss. A true 9 twist barrel won't work with a 75/77 grain bullets. the catch is that many barrels that are marked as 9 twist barrels are actually 8.5 twist barrels. thats why you hear conflicting stories about 75/77 class bullets in a 9 twist barrel.
I guess I've never checked the twist-- will do the next time I clean it as I suspect it may be faster than marked from what I've heard from you and others
 

Kevin Thomas

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The perils of buttoned barrels. I normally expect to see as much as +/- one inch from the stated twist in buttoned barrels. Unfortunately, it's sort of a crap shoot as to whether the variation will be on the "fast" or "slow" end of the listed twist.

Always opt for the faster of two twists if you think it's anywhere close to being marginal. Too fast a twist (even when it's a bunch too fast) will almost never cause a prblem; too slow a twist will ALWAYS case a problem.
 
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