AR twist rate Help please?

[leatherneck448]

Hi, I've been trying to buy an AR parts kit, and I was trying to decide between 1-9 and 1-7 twist rate.
What are pro's and cons of each?
Of course, 1-7 is going to be better for heavier bullets but with my shooting style (more plinking, perhaps some 3-gun on down the road) I think im going to shoot lighter bullets for the most part (55-62gr.) but is the versatility still worth the money if I decide to shoot 75's later on down the road for yotes' or something of the like? do you think it would be worth it to save 45 bucks more and get a chrome lined 1-7 twist barrel?

Thanks,
Kenny

 

[AR27]

I have a 20 inch bcm upper with 1/7 and a guy at the range told me that its to much for 55gr out of a 20". I didnt know if it is true but something to consider.

 

[G27RR]

If you can get a 1:8 barrel, it's kind of the sweet spot for a wide range of bullet weights. If your plinking ammo is 55gr and up, the 1:7 should still be fine and gives you more flexibility than the 1:9. The difference is a little overblown in my experence unless you need maximum accuracy.

 

[husker]

I have no probs at all shooting 55 grain Pmc bronze out of my 1/7 twist AR

 

[leatherneck448]

If i dont really need a super-accurized rifle, is it still ok?
Say if I got a 1:9 twist rifle, would a 75 grain bullet still get MOA accuracy out of that barrel, or is a 1:7 needed for that sort of application?

 

[Canuck-IL]

69gr and up is a crap shoot with a 1:9 - - I've seen lots that were fine with 75s but a few that weren't. A 55gr should be fine in a 1:7 - the issue with fast twist barrels is only apparent when shooting very thin-skinned varmint bullets which tend to be the very lightweight ones. Both my 1:7s do OK with good 55s out to 200 yards.

Get the 1:7 and don't think about it again.
/Bryan

 

[jerkface11]

What canuck said. Some 1:9's shoot heavy bullets and some don't. You don't lose anything by going with a 1:7 though.

 

[W.E.G.]

Unless you plan on shooting 80-grain handloads that won't fit in the magazine anyway, it won't matter one whit whether you get the 1:7 or the 1:9.

1:9's seem to be just a little bit cheaper than 1:7's if that makes any difference to ya.

Most folks who buy their first AR run out and buy the cheapest 55-grain ammo they can find anyway.

 

[Skylerbone]

The chrome lined barrel won't do your accuracy any favors, jury out on how much it REALLY affects it. If you can't get a 1:8 then stick to the 1:7 or plan on a lighter bullet. I shoot the 60 gr. A-Max in my 1:9 but that's mine. Likely your accuracy will depend on the quality of the barrel (something AR guys here can help you with as far as vendors go) and your own level of ability.

Twist is just another part of the equation to add to bullet weight, velocity of the projectile, length of barrel and all the rest. If you know what you want to shoot ie. factory loaded Federal Brand xx gr. through a xx" barrel for coyote it might give people more insight for their suggestions.

For general plinking, SD, HD and easy availability of FMJ ammo 1:7 really is ideal.

 

[Zerodefect]

I prefere 1/7 for my 5.56 carbines (14.5-16") and 1/8 for 5.56 rifles (18-20").

 

[J.Boyette]

Twist rate.

I have two 1/7's, one 1/9 and at work we use 1/9's in all the rifles.

So if I was you, if you plan on shooting alot of targets under 300yds with bullet weight around 55grn + or - 8 grns 1/9 is just the ticket.

If you plan on shooting out to 300yds to 600yds go 1/7.

I shoot the Fed 55grn American Eagle red box stuff to 500yds all the time in a 1/7 18" and 16"

John

 

[GCBurner]

My Colt HBAR has a 1:9 twist, and shoots its best groups with 62 gr. SS109 ammo. I tried some 69 gr. Speer ammo, but the Lake City SS109 still topped it. I wish now I'd bought a whole case when it was available.

 

[GunTech]

If you mostly shoot surplus ammo, 1:9 is the best compromise for both M855 and M193. The main reason for the 1:7 twist was to stabilize the new tracer. Most of us don't bother with tracer. As noted, if you want to shoot the really long bullets you'll need at least 1:7. If you only shoot lights, the original M16s has 1:12.

Here's a precision comparison (i.e. groups size) with various twists shooting M193 and SS109 (M855) based on Army studies.

 

[BushyGuy]

i prefer 1:9 twist, i feel 1:7 is way too fast. 1:8 is a good compromise between the two ( if you can find one).

 

[TonyAngel]

If you want to be safe, go with the 1:7 twist. The only problems that you might have with the faster twist is with the super light varmint bullets, like the 40s and under. Mine doesn't have any problems with 45s. The other problem, if you want to call it that, is that it MAY not shoot lighter (62gr and under) cheap ammo as well as a 1:9 twist. By cheap ammo, I'm talking about all of the steel cased stuff and the various military type stuff. M193, M855, SS109, etc. is crap ammo in terms of bullet quality. The theory is that spinning a crappy, off balance bullet faster just makes it wobble more. Whether you will notice it, I don't know. Odds are that it won't matter enough to make a difference.

On the other hand, my 1:9 carbine shoots 77s just fine.

BTW, the appropriate twist rate for any projectile is defined by the bullet's length, not its weight.

 

[TonyAngel]

What "parts" kit are you considering buying anyway? There's a lot of crap out there.

 

[Bartholomew Roberts]

Another good Army study discussing twist rate and how it affects accuracy with various loads out to 300yds: http://thefiringline.com/forums/showthread.php?t=401831

Short summary: a 1:7 twist shoots 55gr military ball ammo just as accurately as a 1:12 twist at 300yds.

On the 1:9s, some will handle 68gr up well and some won't. I've watched an Armalite 1:9 with chrome-lined barrel shoot great with Hornady 75s (1"). The same load in my Bushmaster 1:9 HBAR - 4-5" at 100yds.

 

[rattletrap1970]

I have a .223 Savage (yeah, not an AR) and it will not stabilize anything under a 69gr bullet. I haven't used anything heavier yet. It really likes the 69gr Sierras.

 

[raz-0]

From my practical experience, if you want to go 16", 1:7 is what you want. In 20" it is a lot more debatable, but most decent barrel makers for the AR seem to be going with 1:8 for 18-20 inch barrels.

As far as I can tell from some of mine and my friends project guns getting rebarreled lately, you get a bump in performance if your bullet is making two complete revolutions before reaching the crown. Both 16" and 18" shoot 55gr fine at 1:7 and 1:8.