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Posted: 3/6/2006 8:41:36 PM EDT
I was talking to some dude who was on rifle shooting teams when he was in the Navy and he told me that a 1X7 twist is too fast for 55 grain M193. He didn't say that it was so fast that the bullet spun apart, but he said that the bullets were spinning so fast that somehow the groups opended up.

Now I don't know what legnth barrel he was shooting, but he said that guys w/ 1X12 A1s were shooting better than the guys w/ 1X7s w/ the 55 grain military ammo. He also mentioned something about the shape of the bullet, I guess the spitzer military bullet profile being affected by too much rotation???

What is your experience w/ this stuff, b/c I like to stockpile M193 as bulk quantity SHTF ammo, but I preferr my AR w/ a 1X7 for shooting new heavy tactical loads for defense.
Link Posted: 3/6/2006 9:31:51 PM EDT
Many people shoot M193 spec ammo thru 1:7 barrels without this problem. Each barrel is different, even with the same make, model and twist rate.

TS
Link Posted: 3/7/2006 5:40:51 AM EDT
The difference in shooter ability is FAR greater than the difference in accuracy potential between a 1:7 twist and a 1:12 twist shooting M193.

While some believe that is an "optimum bullet weight" range for a given twist, I do not. My experience shows that every barrel is different, and some barrels will have specific bullets and charges they shoot well, some they wont.

When it comes to twist rate and bullet weight (length), twist will have an impact.... but for the most part, you are either stabilizing the bullet, or you arent.
Link Posted: 3/7/2006 7:51:56 AM EDT
I had an HBAR 1/7 twist in the late 80's and early 90's. It seemed to like bullets that weren't as spire pointed as others. There was a UMC round that worked great until they changed it. None of them shot really bad but those would fall within and inch.
JRandyH
Link Posted: 3/7/2006 7:53:29 AM EDT
Considering that some people in this board have obtained sub-MOA groups with their handloaded 55gr ammo and 1:7 barrels I don't think the idea that 1:7 is "too fast" has any merit. Some people have reported that with some very fragile bullets the bullet comes apart at very high velocities out of 1:7, but even then, quite a few shooters use 45 and 50 gr varmint bullets out of their 1:7 rifles, with good results.
Link Posted: 3/7/2006 9:35:49 AM EDT
Ask LMT about it?

Alot of good info !! But went over my head

Theres alot of m193/55fmj shot out of 1/7 twist!
Link Posted: 3/7/2006 1:25:45 PM EDT
My most accurate ammo at 100-200 yards is a 53 grain Hornady JHPBT Match bullet shot out of a 1/7 Colt BBL. I don't bother shooting it past 300 [don't have many ranges that far anyways around here] as the heavier rounds will do better the further out you go but for what I mostly shoot it's very accurate.
Link Posted: 3/7/2006 2:14:13 PM EDT
I've never seen really poor accuracy from a 55gr bullet out of any 1/7 twist barrel. I have a Colt 6600 Green Label (20" 1/7 HBAR) that shoots tight groups of 55gr WWB at 100 m. Granted, some definately shoot better than 55grains (my most accurate load for this specific rifle is the 75gr Match HP from BH at 200-300M and beyond). However, I know from personal experience what happened when I shot 40 grain varminter rounds out of a 20" 1/7 HBAR - many bullets spun themselves apart and were keyholing targets just 50 meters away. But Ive never had problems from bullets over 52gr in any 1/7 twist barrel Ive ever owned.
Link Posted: 3/7/2006 3:45:25 PM EDT
I don't know how well you can see these, but these are groups from a bone stock Colt 20" A2 with a 1/7 twist. The ammo is black hills blue 52 grain BTHP. I did have a leupy scope on an arms #2 mount with crappy rings to test the accuracy. The 52's have been very accurate in both my AR's the other one has a 1/8. I hate to put down the knowledge of a military personelle but in this subject, your buddy is "full of crap".





I have found many military personelle to have much less knowledge than I do when it comes to the weapons they have used. It is ironic but they probably haven't had time and the resources to study it to the point that I have. There are however, many military people that know much more than I do also. Everybody is a different level as far as knowledge goes. Obviously.
Link Posted: 3/7/2006 3:52:36 PM EDT
Ammo Oracle....
Link Posted: 3/7/2006 4:22:24 PM EDT
GOOD SHOOTING
Link Posted: 3/7/2006 5:00:53 PM EDT
I'll reiterate what everyone else has said. The idea that "1:7 twist can't shoot 55gr" is pure BS.

I've never seen anyone provide proof of either this or the similar idea that "55gr. is more accurate in a 1:12 twist than a 1:7".

Many people have shot 55gr. ammo out of a 1:7" twist barrel with no problem, myself included. I shoot 52gr. Hornadys out of my 1:7" twist barrel, and off the bench all the bullets will go into the 10" of the 100yd reduced target. 1:7" twist is plenty accurate for me.
Link Posted: 3/7/2006 7:53:46 PM EDT

Originally Posted By FMJ:
GOOD SHOOTING



Thanks man. I'm getting better, but those stock triggers are pretty heavy. Especially when you compare them to those RRA NM 2 stage triggers!!!
Link Posted: 3/8/2006 6:53:03 PM EDT
I am a member of the All Guard combat team, we use 55gr ammo exclusivly for major matches. it is far more consistant than the 855. in most of our box stock M16A4 it will hold around 2moa with good lots of 55gr all the way back to 500yrds. think about it a 10 inch group at 500 yrds with 55gr ammo, 1/7 twist barrel, rack grade m16a4 with the crappy burst trigger, no float tube and iron sights or trijicon tao1nsn isn't too bad.

you should try shooting full distance NMC with a rack grade AR, m855 ammo. No coat, no mat, GI web sling. now there is fun. will really make you appreciate your match tuned AR.
Link Posted: 3/8/2006 7:02:46 PM EDT

Originally Posted By P-245:
Ammo Oracle....



Yep

Q. Will M193 be accurate in a 1:7 or 1:9 twist barrel?

It may be marginally less accurate due to the fast twist rate, particularly in 1:7 twist barrels. Unless you're trying to use these rounds for benchrest shooting, though, it shouldn't be enough to matter.

A bullet's flight is disrupted slightly as it leaves the barrel and after traveling some distance, will "settle down" into an even spiral, similar to a thrown football. The faster a bullet is spinning, the longer it takes to settle down. The most accurate twist rate for any length of bullet will be just a bit faster than what is required to stabilize it for its entire flight path (1.3 SG). But note that bullet quality plays a much bigger part in this equation. A uniform bullet will spin true; a non-uniform bullet will wobble and be inaccurate. As a general matter when shooting M193 or M855 (as opposed to match ammo) its better to err on the side of a faster twist rate. Regardless, both 1:9 and 1:7 twists seem to shoot M193 and M855 very well.
Link Posted: 3/8/2006 8:00:20 PM EDT

Originally Posted By sgtscott:
I am a member of the All Guard combat team, we use 55gr ammo exclusivly for major matches. it is far more consistant than the 855. in most of our box stock M16A4 it will hold around 2moa with good lots of 55gr all the way back to 500yrds. think about it a 10 inch group at 500 yrds with 55gr ammo, 1/7 twist barrel, rack grade m16a4 with the crappy burst trigger, no float tube and iron sights or trijicon tao1nsn isn't too bad.

you should try shooting full distance NMC with a rack grade AR, m855 ammo. No coat, no mat, GI web sling. now there is fun. will really make you appreciate your match tuned AR.



+1

Shoot tons of genuine issue LC M193 & M855 and M193 is more accurate and consistant with some LOTS being exceptionally good.
I shot my Issue A2 last season at a XC practice match to get some good zero's for CNGB & WPW and shot a 440 something using M855 wearing BDU's and a hasty sling. Dropped most points at 600 as that shitty ammo uses all the black ! My avg with my match service rifle AR is 478-480.
Link Posted: 3/8/2006 8:00:43 PM EDT

Originally Posted By sgtscott:
I am a member of the All Guard combat team, we use 55gr ammo exclusivly for major matches. it is far more consistant than the 855. in most of our box stock M16A4 it will hold around 2moa with good lots of 55gr all the way back to 500yrds. think about it a 10 inch group at 500 yrds with 55gr ammo, 1/7 twist barrel, rack grade m16a4 with the crappy burst trigger, no float tube and iron sights or trijicon tao1nsn isn't too bad.

you should try shooting full distance NMC with a rack grade AR, m855 ammo. No coat, no mat, GI web sling. now there is fun. will really make you appreciate your match tuned AR.



Do you guys actually use your slings? And if you do, How do you deal with the POI shift? I emember resting my Stock A2 Govt on an ammo can one time and I put some pressure on it and it changed the POI enough at 50 yards that it was frustrating. Now, the groups weren't all that bad it's just that it moved enough for me to not be shooting right on. Probably I'd say about a little over 2" and it was high and right. I'm bettin if you get all slinged up and tight, it's going to pull your poi down some. I'm just curious how you do it. And no, 10" groups at that range with that equipment is more than fairly good, that's just downright terrific!!!

Sorry to hijack the thread.
Link Posted: 3/8/2006 8:28:34 PM EDT
[Last Edit: 3/8/2006 8:38:14 PM EDT by tonybelding]
I believe the high twist rate could cause accuracy problems for light bullets -- but only at extended ranges. By that I mean 400+ yards. Then you might see bullets starting to "lurch" out of their expected path, because their direction of travel has deviated too much from their axis of rotation. You can shoot 100-yard groups all day long and never see this effect. It's questionable whether you'd even see it at 300 yards.

With a slower twist rate, the bullet is less over-stabilized, and it has an opportunity to aerodynamically change its pitch to better match the trajectory curve. Thus there is no random "jump" required to correct that mismatch.

Keep in mind, this is only how it was explained to me years ago. . . I haven't done enough long-range shooting to prove it.

Also in the realm of hearsay -- I recall reading a claim that the original 1-in-14" twist rate was ideal for long-range accuracy with M193 ammo, and that 1-in-12" twist was tight enough to cause the "jumping" effect at long ranges! But the change to a tighter twist rate was required so that bullets would be stabilized in sub-zero weather. The Army, reasonably enough, wanted a rifle that would work anywhere on Earth, including the arctic.
Link Posted: 3/8/2006 9:11:47 PM EDT
max loaded 55grn V-MAX fragment in less then 20ft out of my SL8-1 w/ 1x7 twist. paper looks like a .410 loaded with quail shot hit it. XM193 is ok though...fmj?.. not too accurate past 150yrds. at least not nearly as with heavier bullets 62grn+. im reloading sierra gameking 65grn spbt which works well between both the 1x7 and the 1x9.

Link Posted: 3/9/2006 4:34:40 AM EDT
[Last Edit: 3/9/2006 4:44:33 AM EDT by FALARAK]

Originally Posted By tonybelding:
I believe the high twist rate could cause accuracy problems for light bullets -- but only at extended ranges. By that I mean 400+ yards. Then you might see bullets starting to "lurch" out of their expected path, because their direction of travel has deviated too much from their axis of rotation. You can shoot 100-yard groups all day long and never see this effect. It's questionable whether you'd even see it at 300 yards.

With a slower twist rate, the bullet is less over-stabilized, and it has an opportunity to aerodynamically change its pitch to better match the trajectory curve. Thus there is no random "jump" required to correct that mismatch.

Keep in mind, this is only how it was explained to me years ago. . . I haven't done enough long-range shooting to prove it.

Also in the realm of hearsay -- I recall reading a claim that the original 1-in-14" twist rate was ideal for long-range accuracy with M193 ammo, and that 1-in-12" twist was tight enough to cause the "jumping" effect at long ranges! But the change to a tighter twist rate was required so that bullets would be stabilized in sub-zero weather. The Army, reasonably enough, wanted a rifle that would work anywhere on Earth, including the arctic.



That all smells of pure BS to me. I have shot M193 at 530yd's out of a 1:7 govt profile (M16A2) barrel and never detected any "lurching"
Link Posted: 3/9/2006 4:40:01 AM EDT
You tell them
Link Posted: 3/9/2006 4:54:24 AM EDT
If it's B.S. then we better ask the maintainers of The Ammo Oracle to remove it from their page, because they've got basically the same explanation, including a diagram showing how the problem arises:

http://www.ammo-oracle.com/images/overstable.jpg
Link Posted: 3/9/2006 5:16:10 AM EDT

Originally Posted By tonybelding:
If it's B.S. then we better ask the maintainers of The Ammo Oracle to remove it from their page, because they've got basically the same explanation, including a diagram showing how the problem arises:

www.ammo-oracle.com/images/overstable.jpg



No, not really. The Ammo Oracle only states this in reference to that picture:


You can also overspin projectiles and cause overstability. This results in the not-so-desirable condition that keeps the nose of the round pointed high, as illustrated below:


Note - nothing about "lurching", "path changes", or "jumping". Just the nose being kept pointed higher during the flight path. It doesnt describe what ranges where this has a serious effect.

So, since we are quoting the Oracle:


Q. OK, that's complex. Simple question: Can I fire M193 ammo in my 1:7 or 1:9 twist barrel?

Yes.

M193 is essentially a "universal" round; able to be stabilized by barrels with twists between 1:14 and 1:7. Point of impact will change slightly compared to an M855 zero, so rezeroing is recommended.



Q. Will M193 be accurate in a 1:7 or 1:9 twist barrel?

It may be marginally less accurate due to the fast twist rate, particularly in 1:7 twist barrels. Unless you're trying to use these rounds for benchrest shooting, though, it shouldn't be enough to matter.

A bullet's flight is disrupted slightly as it leaves the barrel and after traveling some distance, will "settle down" into an even spiral, similar to a thrown football. The faster a bullet is spinning, the longer it takes to settle down. The most accurate twist rate for any length of bullet will be just a bit faster than what is required to stabilize it for its entire flight path (1.3 SG). But note that bullet quality plays a much bigger part in this equation. A uniform bullet will spin true; a non-uniform bullet will wobble and be inaccurate. As a general matter when shooting M193 or M855 (as opposed to match ammo) its better to err on the side of a faster twist rate. Regardless, both 1:9 and 1:7 twists seem to shoot M193 and M855 very well.

Link Posted: 3/9/2006 9:09:22 AM EDT
+1
Link Posted: 3/9/2006 12:42:31 PM EDT
yup we use the sling with the iron sights, be sure to use the same tension each time. if you are shooting a scoped rifle, do your best not to let anything touch the handguards. i use Mag on ground when allowed, or by gripping only the magwell. resting the handguards on anything while using a scope can throw shots all over the place. My first year at AFSAM my 300 prone rapid got pulled right out of the black because of hand placement on the handguard. The iron sights are less affected by this pressure because the front sight moves with the barrel.
Link Posted: 3/9/2006 2:52:05 PM EDT
The only thing that could cause divergence from straight flight in a spinning bullet is a noticable lack of concentricity in the bullet. If its mechanically spun axis is not pretty close to its mass axis, it could spin effectively in a circle. But it's really hard to do that with such small bullets... REALLY hard.
Link Posted: 3/9/2006 3:43:46 PM EDT
[Last Edit: 3/9/2006 3:44:41 PM EDT by JJREA]

Originally Posted By sgtscott:
yup we use the sling with the iron sights, be sure to use the same tension each time. if you are shooting a scoped rifle, do your best not to let anything touch the handguards. i use Mag on ground when allowed, or by gripping only the magwell. resting the handguards on anything while using a scope can throw shots all over the place. My first year at AFSAM my 300 prone rapid got pulled right out of the black because of hand placement on the handguard. The iron sights are less affected by this pressure because the front sight moves with the barrel.



Once I got smart about it, I was alot more careful when benching it with a scope on. I do however put a rest under the handgaurds, as close to the receiver as possible and let it sit there, just real nice. Not putting any downward pressure on it. I think it works OK. I really am interested in you shooting with a sling and the irons and the change of POI. I'll do some testing with mine. I don't know if I can use the same amount of pressure each time. We plan on doing some longer range shooting this summer so I'll see if I can even come close to matching your results. 10" at 500, wow!!!! I have to find a load that my 20" a2 likes. It hated Q3131A, but I may have to try some of the Q3131. And we got a bunch of adcom m855 and I'd like to see how that does. Thanks for the input.
Link Posted: 3/9/2006 11:20:49 PM EDT
[Last Edit: 3/9/2006 11:31:51 PM EDT by NYPatriot]
www.jimwardrip.com/firearms/556_Ballistics.htm

The increase in projectile length, weight, and configuration of the M855 bullet requires different twists in the barrels, lands, and grooves to stabilize the bullet in flight. The M16A1 has a 1:12 barrel twist (the bullet rotates once for every 12 inches of travel down the barrel). The M16A2/A3/A4 and the M4 carbine has a 1:7 barrel twist (the bullet rotates once for every 7 inches of travel down the barrel).

The M16A1, with its 1:12 twist, does not put enough spin on the heavier M855 bullet to stabilize it in flight, causing erratic performance and inaccuracy for training or full combat usage (30.48- to 35.56-centimeter shot group at 91.4 meters and 72-inch shot group at 274.2 meters) (Figure 2). Although firing the M855 cartridge in the M16A1 rifle is safe, it should only be used in a combat emergency, and then only for close ranges of 91.4 meters or less.



Figure 2. Ammunition impact comparison.

The M16A2 rifle with its 1:7 twist fires both types ammunition with little difference in accuracy to a range of 500 meters. The M16A2 and its ammunition are more effective at ranges out to and beyond 500 meters due to a better stabilization of the round.

The two 10-round shot groups in Figure 2, A were fired by a skilled marksman at a distance of 274.2 meters using the same M16A1 rifle. The 25.4-centimeter shot group on the left was fired (and zeroed) with M193 ammunition. The 6-foot shot group on the left was fired with M855 ammunition.

Figure 2, B shows two 25.4-centimeter shot groups fired by the same skilled marksman at a distance of 274.2 meters using an M16A2 rifle. The shot group on the left was fired (and zeroed) with M855 ammunition. The shot group on the right was fired using M193 ammunition.

As stated previously M193 and M855 ammunition can be fired from an M16A2-/A4-series weapon. Table 1 and Figure 3, show the difference between a rifle zeroed with M855 ammunition and then re-zeroed with M193 ammunition at 300 meters. There is practically no difference between the trajectory of the rounds or the impact of the rounds on target.

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