Ammor advice ref AR15 HBAR Sporter

M

Mike Spight

New member
I have a pre-ban Colt, AR15 HBAR Sporter. Although I originally sighted it in w/Winchester USA Ball ammo (55gr), isn't this rifle (like the M16A2) actually designed to shoot the 65gr projectile? If so, how much accuracy potential am I losing w/55gr ammo? Although I plan to order a case of the 65gr stuff (if that's what the rifle is set up for based the rate of twist) I still have some of the 55gr stuff that came with the rifle when I purchased it a few years ago. Any advice/info will be greatly appreciated!

[This message has been edited by Mike Spight (edited April 22, 1999).]
 
I believe the bullet weight is 62gr and they are for barrels with a 1/7 or 1/9 twist. Using 62gr bullets in a barrel with a 1/12 twist may not stabilize the bullet properly, resulting in keyholing.
 
Mike,

Destructo is correct that the Wieght is 62 grn.
As he stated, the important thing is the spin, not the thickness of the barrel.

As for which spin goes with which round, I thought the AR was originally designed with slower spins for the lighter bullet, for more potential wounding power.. but I can never remember exactly, so I stick with the middling 1/9 or 1/10 rates, as I use both wieghts of ammo in my ARs.

(EDIT: Kodiac is correct below.. "higher" numbers = slower spins.. my brain fart..)

[This message has been edited by Rob (edited April 22, 1999).]
 
I believe the original twist was something like 1/14. At that rate a 55gr bullet was pretty unstable and tended to tumble as soon as it hit anything. Some people liked this feature (SF guys), but the Army (if memory serves) wanted a little more accuracy which necessitated a tighter twist.
 
Rob/Destructo/Kodiac: Thanks. Will try the 62gr stuff...actually, the rifle still shoots quite accurately w/the 55gr bullet...might as well try to optimize, though.
 
Actually, the slower twists stabilized the 55gr pill just fine. The 1/7 twist was necessary to stabilize the heavier 62gr pills. The 1/9 twist seems to be a workable compromise that stabilizes both equally well. The close encounter distances in the jungle environment led to the unauthorized practice of cutting a couple of "hounds teeth" in the crown of the muzzle. The teeth were nothing more than a couple of cuts with a three-cornered file, usually in the top part of the crown. This caused jets of gas to spew upward as the bullet exited the muzzle, creating a pressure differential at the base of the bullet which pushed the base downward and began an immediate destabilization and subsequent tumbling of the projectile. Result was the equivalent of a high speed piece of shrapnel, instead of the neatly drilled hole of a FMJ bullet as envisioned by the Geneva Convention. A field expedient MWO if you will...
 
Thanks to all for the input. To add to my confusion on this issue, ar15.com section on barrels indicates that the 1 in 7 twist rate is suitable only for "...heavier, custom bullets around 87gr..." or words to that effect. They indicate that the 1in9/1in10 is probably the best all round twist rate for everything from 52gr to 65gr bullets. My AR16 is (as stated) a pre-ban Sporter Match HBAR...according to data on ar15.com, it comes with a 1 in 7 twist rate. If it is (really) suitable only with heavier, custom bullets and ammo, guess I'm going to be looking for a re-barrel job at around 1in9 so I can shoot factory stuff from 55gr to 62gr.
What do you think?
 
I was laboring under the impression that the 1/7 twist would stabilize both 55gr and 62gr equally well with a slight loss in velocity over the 1/12 twist.
 
Mike I get from your post that you do not know which twist your AR has. Mine says 1/7 NATO right on it, I thought all AR 's did?

Later
Daren
 
Mike. According to the latest issue of Petersons Rifle Shooter, the military has standardized on a 70 gr. bullet. The article is by Col Craig Boddington, USMCR. I think you would need the 1 in 7 inch twist for that one.
Paul B.

COMPROMISE IS NOT AN OPTION!
 
Mike,
The length of the bullet has more to do with the right twist rate then the weight. The 1/7 twist was adopted to stabilize the M856 tracer round. 1/9 is fine for the M855 ball ammo (62 gr). You can shoot the M193 and M196 (55 gr ball and tracer) in the 1/7 inch barrels with very good accuracy. You can't go the other way though, no M855 or M856 in the 1/12 twist barrels.

A little on history. The AR15 was originally designed with a 1/14 twist barrel. This did not get the accuracy the Army wanted in the subzero climate of the Arctic Test Center. A change in twist to 1/12 was one of the first things the Army specified. The AR15/M16 had a 1/12 twist barrel until the adoption of the M16A2.
 
Mike Spight:

I have a Colt AR-15A2 20" Gov't model pre-ban which I have used with 55 gr FMJ since 1989. I have shot decent groups (in the 10 ring or better 4 out of 5 shots on a 25 yard pistol target) out to 200 yards with the 1 in 7 twist both off the bench and in urban carbine classes.

In my unscientific shooting of water-filled jugs, the cartridge still goes violently K-SPLATT shedding jacket and breaking up by the time it goes out the aft end of the split-open jug. Entry hole is a nice neat .22 hole BTW.

In summary, unless I am shooting High Power competition and want the absolute TIGHTEST in groups (for which I will probably use .308 because my druthers for .308 for extended range), I think plain 55 gr FMJ in the 1 in 7 is just fine for personal defensive long arm usage.

Edmund

PS: Mike: Into martial arts training AND rifles? Sounds like you plan to have all the bases covered! My hat's off to ya.
 
Edmund et al: Thanks again for all the good advice. I also exchanged e-mail w/Michael Jones who does the AR15 Models section on ar15.com. He stated that my rifle's barrel did have a 1in7 twist rate and would certainly shoot 55gr at an acceptable (but not optimal) level of accuracy. He also stated that to optimize accuracy, I'd need to go with heavier bullets. As I don't currently handload 5.56mm, I've been shooting 55gr factory. Will now try a factory load w/a heavier bullet in the 62-65 gr range (if available).

Yeah Edmund, I try to keep my hand in this stuff...between my fellow soldiers, LEO friends, fellow IDPA shooters and the posters on this site, it fairly easy (and enjoyable) to do.

Darren: I can't find "1in7 NATO" stamped on my rifle, but I didn't remove the handguards. Will check later tonight.

Jeff: Like I said, the rifle shoots 55gr pretty well...seems like I'm getting different advice from different folks (which is not bad). Guess I'll just have to try some 62gr and see if it outperforms the 55gr. If it doesn't, well the 55gr is a LOT cheaper than anything else around, so that's good!

[This message has been edited by Mike Spight (edited April 26, 1999).]

[This message has been edited by Mike Spight (edited April 26, 1999).]
 
In my somewhat limited experiences helping feed a friend's 1:7 HBAR, bullet quality is far more important than weight and alleged "over-stabilization" of lighter bullets.

BTW, Jeff is right on re: inadequate bullet stabilization at below-freezing temperatures. One source I've seen even says that 1:9 barrels marginally stabilize the 62-gr NATO bullets somewhere below 0° F. And I tried SS109s once in a 1:12 barrel and found keyholed bullet strikes in about a 10-inch shotgun-style pattern at only 100 yards.

PMC/(Speer?*) 62-gr. FMJBTs never grouped any better than Win. 55-gr. FMJBTs out of that HBAR. 2 MOA best, never worse than 3 MOA, with four different loadings using WW748.

Sierra 69-gr. Matchkings, however, did 1- to 1.25 MOA, iron sights and a sloppy sandbag rest.

Do Sierra or Hornady make a 62- or 63-gr HPBT Match bullet yet? I'd gladly use those at 200 & 300 all the time.

*Bought some major-brand 62-gr pills and they were made in Israel. Think they were Speer, but that half-box is not handy right now...

[This message has been edited by Cheapo (edited April 26, 1999).]

[This message has been edited by Cheapo (edited April 26, 1999).]
 
Cheapo: Thanks bud...sounds like I probably won't be able to tell that much difference between 55gr and 62gr factory stuff. Might try anyway when I have some extra time.
 
You must log in or register to reply here.
Back
Top