1:7 vs. 1:9 twist

[al1599]

I was just wondering about some stuff I heard for AR-15 barrels. I've heard the 1:7 wear out faster than a 1:9. I'm fairly new to the gun world so I try to clear things up when I hear them. And also which one will be able to shoot a 62 grain bullet sufficiently? Thanks in advance for anyone answering the questions. You guys and ladies help me out tremendously.
Alvin

 

[nbkky71]

All shooting causes wear on the barrel but I too have heard that tighter twist rates will accelerate wear. I doubt that you will be able to tell any appreciable difference in the amount of wear between and 1:7 and a 1:9 barrel.

I'd say that the the amount of wear you see will be dependent on the ammo that you shoot. Higher velocities tend to accelerate wear on the barrel/throat

Either twist rate will stabilze the 62gr bullet just fine.

 

[Jack A. Sol]

1-9 is ideal for 62 grain. 1-7 will allow you to shoot the heavier stuff with more confidance of accuracy, but will not let you shoot the <50gr stuff

 

[Lonestar.45]

Everything you ever wanted to know about ar-15 twist and bullet weights, right here:

http://www.ammo-oracle.com/

 

[Onmilo]

If you are planning on shooting the rifle on full auto or burst setting and are also planning on loading a tracer round every third cartridge, then yes, yhou will experience accelerated barrel wear with a 1-7 twist barrel.

If you plan on shooting like the majority, you will notice an improvement in accuracy with heavier bullets in the 1-7 twist along with slightly reduced lethality of bullets of 55 grains or less and of full metal jacket construction.

The 55 grainers overstabalize in the 1-7 twist and act like little drills on soft targets, boring right through instead of yawing and fragmenting like they are supposed to.

If you plan on shooting bullets of 50-69 grains a 1-9 will do fine.
If you plan on shooting mainly bullets of 60 to 80 grains a 1-7 twist is a better choice.

I now own rifles with both twist rates and I also own an AR15 rifle with a 24" barrel with a 1-10 twist rate which I shoot nothing but cartridges with bullet weights of 45-52 grains with most excellent results.

 

[Warbow]

Onmilo wrote:

The 55 grainers overstabalize in the 1-7 twist and act like little drills on soft targets, boring right through instead of yawing and fragmenting like they are supposed to.

The math says that myth is false.

 

[Don't Tread On Me]

1] Gee, I've never seen this topic before

2] Like clockwork, this thread has already produced at least 3 thoroughly debunked, yet widely circulated myths.

 

[KFDiesel]

Why dont you quit critisizing and start posting something, anything that is worth reading. Im sure you can find this topic in search but one of the great things about THR is just browsing. These topics come up but if you havent been on for a while you might have missed a thread. I didnt really have a question per say about twist rates in an AR but Ive ejoyed reading this and thinking about it even tho some of the opionions are widely circulated myths. Now why dont you post a question or try to help someone here by trying to answer something if you know anything.

 

[Onmilo]

Oh, the math from the wizards at ARF.com.

My experience is based on shooting living, breathing critters with the cartridges and twist rates in question.
The results on flesh debunk the math.

Ever wonder why some guys complain that the M16 isn't effective at knocking bad guys down and other troopers have no complaints about the effectiveness?
Ever wonder exactly what kind of ammunition they were using in what twist rate at the time they had their good or bad experience?

 

[RugerOldArmy]

Onmilo, some of what you posted, based on your experience is correct. 1-9" will work well for bullets up to 69 Gr (and even lower than 50, 40's for example).

But there were a few myths, as DTOM indicated.

- Faster twist will NOT cause more barrel wear, or it least the twist will play an insignificant role. The majority of wear is from the gas cutting in the throat, and/or our cleaning efforts without bore guides. (With respect to the other point, by another poster, 1:7 WILL let you shoot the <50 Gr bullets, and often well. The thinner jacketed bullets may come apart if you push them too fast though.)

-Twist and lethality: Speed and bullet shape (which impacts the necessary twist) come into play. The ammo oracle will cover this better than I, and the link was already posted. But with respect to the 55 Gr bullets, the faster twist might just result in a bit slower velocity in that fast twist barrel, and that might be all you have working to make that point.

- Bullets as drills, I don't think you'll find any reference to support that.

But I do think you can find other references, besides myself and DTOM, to dispel the points I questioned.

We all file away what we hear as truth, and for a while, I was SURE there was a Santa Claus. We should all question the validity of what we hear, against what is reasonable. Including my posts. DTOM was probably just trying to discourage the spreading of myths.

He might have fell for that Santa Claus thing too!

 

[Don't Tread On Me]

Thanks RugerOldArmy, that pretty much covers it. KF, no need for the flamethrower ok?

How come everyone else gets to tease the redundant threads, but the 1st time I ever do in over 2 years someone comes out of the woodwork and lets me have it?

If the shooter is committed to sticking to 69gr ammo and lighter, then there's really no reason at all for a 1/7. Get a 1/9. If you want the ability to stabilize 75 and 77gr ammo out to long distances in freezing cold weather - you'll want that 1/7. I have found no economical bulk quantity ammo in the heavier weights. The Wolf, AE, Winchester, and milsurps are all 55 or 62gr. So as a result, the 1/7 really only comes into play for the use of higher quality match-grade 75 or 77gr ammo. That typically serves as defensive ammo for most people, not practice ammo or blasting ammo due to the prohibitive costs (unless you handload, and even then it's not cheap, but at least doable). I don't know too many people who do rapid fire practice drills with $1 a shot ammo...

That's pretty much the only concern. Barrel wear? Insignificant. If you wear either barrel out - then you've shot about 5-10x the cost of a new barrel through either one. Especially at the price of ammo these days. Lousy Wolf is now $200 a case! 5,000rds going to cost $1,000 w/o shipping. Barrel could do 10,000rds before you might want to chuck it, all depends on your accuracy expectations. $2,000 in ammo has to be spent to make that barrel worthless I would think. Heck, cut that round count in half - and it's still more than twice what a new barrel costs. A good Bushmaster barrel can be bought for $220. Also, after that many rounds, you're looking at a new bolt too and whatever else has worn.


To me, it's a non-issue given what I said above.

 

[Quintin Likely]

I was just wondering about some stuff I heard for AR-15 barrels. I've heard the 1:7 wear out faster than a 1:9. I'm fairly new to the gun world so I try to clear things up when I hear them. And also which one will be able to shoot a 62 grain bullet sufficiently?

I don't know about faster twists wearing barrels out quicker. A worn out barrel is subjective; a "worn out" barrel for a competitive NRA high power rifle shooter is one that's not even broken in for the average joe that does most of his shooting within 100 yards.

1:7 or 1:9 will stabilize a 62 just fine. I say lean on the faster side of twists available, in case you get a wild hair and want to shoot 75 Hornadys or 77 Sierras or something.

 

[hags]

Ever wonder why some guys complain that the M16 isn't effective at knocking bad guys down and other troopers have no complaints about the effectiveness?
Ever wonder exactly what kind of ammunition they were using in what twist rate at the time they had their good or bad experience?

I believe the complaints are based on the effectiveness of the 5.56 round as opposed to any ancillary circumstances.

 

[GunTech]

If you read the Army's after actiuon reports about the 5.56, most of the complaints about the lack of killing/stopping power of the 5.56 come from troops who have never been in combat.

Hmm.

"It is apparent that the close range lethality deficiency of the 5.56mm (M855) is more a matter of perception rather than fact, but there were some exceptions. The majority of the soldiers interviewed that voiced or desired “better knock-down power” or a larger caliber bullet did not have actual close engagements. Those that had close engagements and applied Close Quarters Battle (CQB) tactics, techniques, and procedures (TTPs) – controlled pairs in the lethal areas: chest and head and good shot placement, defeated the target without issue."

http://www.bob-oracle.com/SWATreport.htm

 

[GunTech]

1:9 is a compprmise twist designed to shoot M193 and M855 (SS109) equally well - that's it and nothing more. The following shows shot dispersion vs twist as deterimined by FN duriing testing: