AR 1/9 twist vs 1/7 twist...?

[benEzra]

We also found out since his upper is used, it shoots wolf steel case no problem
while my newer upper can't.

If you aren't already, try shooting some Wolf out of a Magpul PMag and see if it cycles OK, and make sure the bolt carrier and bolt are well lubricated. If it still fails to cycle, make sure your buffer weight and buffer spring are a good match for your barrel length and gas port location (H2 or H3 buffer on a midlength or rifle can cause failure to cycle with Wolf, for example); you might also want to examine your gas key screws for proper staking and have them torqued and staked by an armorer if they're not.

It is possible that is failing to fully cycle with Wolf due to needing to just "wear in", but there are often other additional factors that can be addressed.

 

[TonyAngel]

Man, it seems that this is just a debate that never goes away.

I'll throw my .02 in too. Many seem to lump all 55gr (and similarly weighted projectiles) into one big heap and then make generalizations about a certain twist being able to or not being able to shoot it accurately. Really, if you want to talk about what twist will shoot the M193 the best, I'll get a 1:12 twist. The only reason the faster twist was needed was to stabilize the longer tracer projectiles. Look at the varmint rifles that are intended to shoot light bullets. All of those have 1:12 twists or close to it.

If you are trying to decide between a 1:9 twist barrel or a 1:7 barrel, I'd say it depends on what you are going to be shooting most of the time. If all you're going to be shooting is crap M193 or M855, then get the 1:9. I only say that because the crap bullets coming out of the military spec ammo won't wobble as much because they aren't spinning as fast as they would out of a 1:7 twist barrel. Ideally for M193, I'd get a 1:12 twist. It should do the best.

On the other hand, if you are going to be shooting good ammunition. Stuff loaded with some sort of fifty something grain match bullet and up, then go with a 1:7 twist. Why limit yourself. I shoot a 1:8 twist and it shoot everything from the 45gr. Walmsrt stuff to 77gr SMK very well.

 

[RockyMtnTactical]

It doesn't really matter to most. For me, I own more 1/7's but the 1/9's do fine. I shoot mostly 55gr FMJ anyways.

 

[ugaarguy]

If all you're going to be shooting is crap M193 or M855, then get the 1:9. I only say that because the crap bullets coming out of the military spec ammo won't wobble as much because they aren't spinning as fast as they would out of a 1:7 twist barrel. Ideally for M193, I'd get a 1:12 twist. It should do the best.

That's an interesting opinion, but it's not factual. The DoD's own tests have shown that there is almost no difference in accuracy out to 300 yards when shooting M193 out of an M16A1 (1:12 twist), or an M16A2 (1:7 twist) - this information can be found in the Army M16 Marksmanship Manual. As far as M193 being crap, perhaps you'd like to address the Federal Cartridge Company's XM193 accuracy specification:

ACCURACY: 3-10round groups not to exceed 2.00” mean radius maximum average at 200 yards http://le.atk.com/pdf/XM193.pdf bulletins can be found under http://le.atk.com/general/irl/technicalbulletins.aspx

I wouldn't call MOA accuracy crap: Maybe it's crap to you, but not to me.
ETA:

1/9 is a better twist for almost all commercial ammo.

Again, I have to disagree. A 1:7 twist bbl will shoot M193 with nearly equal accuracy to a 1:12 bbl out to 300 yards. There are also many ammo makers offering 70+ grain ammo; and lighter, yet at least as long, lead free rounds now mandated in some states like California (ex: Barnes TSX, Nosler E-Tip, and Hornady NTX) which need a 1:8 or faster twist to stabilize. Remington, Black Hills, Fiocchi, Federal, and others are all offering MK262 inspired cartridges loaded with 77 grain OTM bullets (Hornady with 75gr OTM).