If I'm thinking corectly BALL ammo is the 55 grain mil spec ammo . Used by all of our military . And a 1/7 twist barrel is what every one uses. BUT the 1/7 twist barrel is for heaver ammo like the tracer stuff . Most people would agree that the 1/7 barrel is for heaver stuff ...... So normaly the military would be using the 55 grain bullet {if i'm correct}. What is the main real reason why military is choosing the 1/7 for there M16's / AR15's / M4's . Is there somthing realy great about the 1/7 that makes it not a normal option for most barrel choices .I know it's a NATO barrel choice. If the 1/7 could over stabilize the 55 grain bullet why would they use it? I own two uppers in the 1/7 barrel twist a M4 and a M16 20inch. I'm just wanting to know the real reason for it ...to get a little more fimiliar with what my barrels can do ...........thanks

Err... I think most units are using the M855 round now which is 62 grains in weight along with the newer tracers. Thus the faster twist is necessary for proper stabilization at extended ranges.

Does that sound good?

Look here>>> [url]http://www.ammo-oracle.com/[/url]

MM419

Here is an excellent post by Dr. Gary Roberts.  This is quoted from another forum so I hope he doesn't mind...[;)]

Whenever you acquire 5.56 mm carbines, there are a couple of things you must decide. First, what barrel twist are you going to use—preferrably, go with 1/7. Next, what barrel length are you going to choose—for a GP carbine, ideally go with 14.5 to 16”. Finally, what are your expected engagement scenarios? Entry, perimeter, sniper support, long range, CQB, vehicles, etc…
For general purpose use with 1/7 twist barrels from 0 to 600 yards, I would choose one of the combat proven 5.56 mm (ie. 5.56 mm NATO pressure loads, not .223 SAAMI pressure loads which run about 200 f/s slower) heavy match OTM loadings: either the Hornady 75 gr TAP using the OTM bullet w/cannelure or the equally good 77 gr Nosler OTM w/cannelure loaded by Black Hills, followed by the 77 gr Sierra Match King OTM—which, while exceedingly accurate, is slightly less reliable in semi-auto and full-auto guns, as it unfortunately does not have a cannelure, as well offering slightly reduced terminal effects. If your expected engagement scenario is at more typical LE distances, say out to 200 yards, then the .223 SAAMI pressure loads are fine. The experimental BH loaded 100 gr exhibits impressive fragmentation, even at relatively low velocities, however, their trajectory is like a rainbow—definitely for use under 150 - 200 yards.

NOTE: For general purpose use, if you are stuck with 1/9 twist barrels, you cannot use the heavy match OTM loads; you need to pick the 69 gr SMK OTM, the 68 gr Hornady OTM, the Winchester 64 gr JSP (RA223R2), and the new Federal 64 gr TRU (223L) JSP loading. You are screwed with 1/12 twists, I would probably choose the 55 gr Federal bonded JSP load (Tactical--LE223T1 or identical Premium Rifle--P223T2) in order to ensure adequate penetration.

If you are going to engage vehicles, then the only .223 loads which effectively penetrate automobiles are the 62 gr Federal bonded JSP Tactical (LE223T3) and the similar 55 gr Federal bonded JSP load (Tactical--LE223T1 or identical Premium Rifle--P223T2). The new Hornady 60 gr barrier penetration JSP bullet is not as effective as the Trophy Bonded Bear Claws. None of the OTM bullets, even the heavy 75 – 100 gr loads, offer good performance through automobile glass. FWIW, contrary to what many believe, 62 gr M855 FMJ also is not very good against glass.

If you must have a short barreled 5.56 mm weapon, such as the Colt Commando, Crane CQB-R, HK 53, HK G36C, etc… and you have a 1/7 twist short barrel, you will find that the 75 gr Horn, 77 gr Nosler, 77 gr SMK, and 100 gr BH loadings offer acceptable performance; with a 1/9 twist, stick with the Fed 62 gr Tac JSP (LE223T3). Remember, your effective engagement distance is significantly reduced compared to the longer barreled carbines.

Bottom line, I feel the versatile 75 gr Hornady TAP OTM and 77 gr Nosler OTM loaded by BH are the best available general purpose loads, as they offer good performance out to 600 yards or so and also are effective in short barrel carbines; the Federal Tactical loads using the Trophy Bonded Bearclaw's are the clear choice when intermediate barriers are present.

All this may be somewhat moot within the next 6-12 months, as there is a new military developed caliber, soon to be commercially available, that is dramatically superior to all existing 5.56 mm loads.


More good stuff...

The original AR15 had a SLOW twist of 1/14; as the M16A1 developed, this was changed to a slightly FASTER twist of 1/12.

The change in twist rate to the TIGHTER/FASTER 1/7 was made with the M16A2 in order to stabilize the long M856 tracer round and had NOTHING to do with trying to, “make the 5.56mm perform "like" the 7.62mm round”. Remember SS109/M855, as well as M856 was originally designed as machine gun ammunition for engaging enemy troops wearing body armor during conventional infantry combat at distances of several hundred meters when fired from the Minimi/M249 SAW. Development of the Minimi and its ammo began some 10 years prior to the M16A2.

As noted previously, the terminal performance problems sometimes noted when M855 in fired from M4 Carbines has little to do with 5.56 mm CARTRIDGE performance and a lot to do with specific BULLET performance—in this case the use of machine gun ammunition in carbines; in its intended role out of the M249, M855 performs adequately.

There is NO controversy as to which twist rate is best, which bullets work the best in each twist rate, and what are minimum barrel lengths—all of these parameters are easily measured and quantified through appropriate testing.

You state, “Personally, I feel that a 16" barrel is the absolute minimum length to consider in the 5.56mm cartridge, and anything under 20" demands the use of a 1-9" twist and light to middle-weight (55 to 64-gr.) bullets.” The military disagrees: M16’s use 20” barrels, Mk12’s have 18” barrels, the SPR-D/Recce a 16” barrel, M4’s 14.5” barrels, and the CQB-R a 10.5” barrel. Contrary to your assertion, they all demonstrate their best terminal performance using 62 to 77 gr bullets and all have 1/7 twists. The 1/7 is clearly the best twist rate available, as it allows use of the widest variety of bullets, including the combat proven heavy OTM’s, as well as the bonded JSP’s. Likewise, numerous LE agencies use 1/7 twist rifles and heavier bullets with excellent success. Also, remember that nearly every .223 load, regardless of bullet weight, has LESS "overpenetration" worries than any other commonly used service cartridges, including the various duty handgun calibers.

Contrary to your statement, switching from 62 gr bullets to the more effective 77 gr bullets has resulted in GREATER accuracy at ALL ranges, as discussed by Buxton ( http://www.dtic.mil/ndia/2003smallarms/bux.ppt ).

7.62 x 39 mm is a good cartridge in carbines like an AK or Robinson RAV02 ( http://www.robarm.com/rav02.htm ); however, in general, it has not been very reliable in AR’s as a result of less than ideal magazines and gas tube fouling from dirty third world ammo.

Help me understand how you can "over stabilize" a bullet?? Would that be like 'over straightening' a bent nail?? I shoot a 7 twist, and would like to know what indicatators to watch for, to determine if I am 'over stabilizing'.

In short We used to use the 55 gn. We went to the 62 gn. be cause the FN minimi used the heavier ammo and we adapted the weapon to follow. Yojimbos ammo choice seems almost to me that it costs more than the damn weapon.
GG

Thanks Yojimbo for the artical thats interesting ...

M855 or does fedral or any other manufacture make a good 62 grain bullet in an affordable round? by the case?

Bullet spins too much, loses control and either tears itself to shreads or is VERY inaccurate at say 100 yards and 'tumbles' in the air.

Read up...[url]www.ammo-oracle.com[/url]

Load your own.  About 2 years ago I orderd 3000 SS109 bullets from weidner's and had an all day party on my buddie's progressive loader...  Just for kickes I even tore one apart and there was the little tungsten penetrator.  Of course, if you are in doubt, a magnet is an easier way to check.  

Would you be so kind as to point out the section of the ammo faq that says an "over-stabilized" bullet is very inaccurate and tumnbles in the air?  I can't seem to find it anywhere.  In fact, I've never even heard of such a thing occurring.  

Ever.

Are you sure you're not confusing "over" and "under"?

hehe, guess I should have looked back through it for the 24th time for the details, but from memory I recalled this pic along with the overspinning and pulling apart of bullets in the air to make my post...

[img]http://www.ammo-oracle.com/images/target2.jpg[/img]

what I get for not checking to make sure...


Edited to add: Here's what really happens for the person who created the thread...

[b]You can also overspin projectiles and cause overstability. This results in the not-so-desireable condition that keeps the nose of the round pointed high, as illustrated below:[/b]
[img]http://www.ammo-oracle.com/images/overstable.jpg[/img]

[b]You can also spin them so hard they fly apart.  That's rare, but it happens if you are dealing with very tight twists and very high velocities.  When fired at 3200 fps in a 1-in-7 twist rifle, a round is rotating at over 300,000 rpm when it leaves the muzzle.  Light, thin-jacketed varmint bullets (i.e., 40gr Hornady TNT or Federal Blitz bullets) often can't take that much spin and will pull themselves apart.
[/b]

I haven't found any US M855, but IMI sells M855 spec ammo as well.  Wideners.com sells this stuff, maybe others as well.  It shoots well.

Well I have never seen a M193 55gr keyhole out of a 20" 1:7, even at 600 yds. A good lot # of LC m193 will shoot quite well " easily M.O.M " thru 1;7 even at 5-600 yds.
 The main reason for the 1;7 was for the long bearing surface of the M856 tracer..

I worked in 2/3 ADA's S-3 Shop for a while at Ft. Riley. We used to make the arrangements for the different Batteries of the Battalion to go to the ranges. This included ammo.

My Battlion shot LOTS of M193 Ball thru our 1/7 twist A2's & never had a problem. Well, I know I and quite a few other guys never had a problem qualifying "Expert" with it, anyway. [X]

And this was on a Computer Scored range, not a "Hook Your Buddy Up!" range...

I even pulled out a copy of FM 23-9 a couple of times to show to some of the Officers in the S-3 Shop that we should ideally be using M855 Ball instead of the M193 Ball(Appendix "F", Section IV. Ballistics). They just shrugged & said that we would shoot the ammo that we were issued. Being a Specialist(E-4), I didn't say another word other than, "Yes, sir."

No, you haven't 'overstabilized' it, you have OVERSPUN it. Overstabilized is a misused and redundant term. You might crank it at such high revs that it becomes unstable again, but that is overspinning, not overstabilizing. If a bullet shot better with a slight wobble than it would running true around its axis, then you could spin it till it didn't wobble any more and be 'overstabilized' for that particular application/purpose..

Yea dont fight with the guenius RimLicker he knows all..he he [argue] if you had any common sense and any physics knoledge you would understand . i guess its just to much for some people . Thanks for making me aware of the 62 grain ill try some .. Ive just purchased 1000 rds of LC FEDRAL XM193 55 grain wish i could have found this out sooner i would have got the 62 grain.. oh well guess it will work fine.. [heavy]

I have shot plenty of M193 thru several 20" 1/7 and 2, 16" 1/7 barrels, and my experience has been 3" groups or better at 200 yards.

You might just be surprised.

But why ? As several people have pointed out, read the ammo oracle. Quote:

Q. That's really complicated.  Simple question: Why is M193 better than M855?

In a nutshell: Advantages of M193 over M855:

   * It costs less, so you can buy more.
   * It's compatible with any rifling twist.
   * It's generally more widely available.
   * It has a slightly flatter trajectory with the appropriate battle zero.
   * It appears to have better terminal ballistics than M855.

Though it isn't a bad idea to keep a couple of magazines worth of M855 in case you need to make a long-range (300+ yards) shot against a "hard" target (a vehicle or other equipment), most folks are better served with M193 for general use.