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 AR-15 Range Report (with pictures): USMC 25m Zeroing Procedure
jimmyhots  [Member]
4/15/2009 11:43:52 PM
Hi all,

I just got a wild hair to write up a range report on my experience using the USMC 25m zeroing procedure to dial in my AR-15. If anyone's interested it can be found here:
http://sites.google.com/site/jimmyhots/usmc25mar-15zero

All *constructive* comments, suggestions, critiques are welcome.

Jimmy
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PUBBOY  [Team Member]
4/15/2009 11:54:06 PM
50-200 BZO is better.
rav3nwulfe  [Member]
4/16/2009 12:05:55 AM
sweet stuff dude. nice work, I just finished writing a paper for school, then scanned over your site, I'll have to check it out more thoroughly later.
jimmyhots  [Member]
4/16/2009 10:09:44 AM
Originally Posted By PUBBOY:
50-200 BZO is better.


Yeah I hear you; I plan on trying the 200m zero next. The 300m zero looked to be slightly simpler to implement to start with, plus I wanted something to compare to before moving to the 200m zero. Once I have more metrics on the 300m, I'll try the 200m. This way I'll have some concrete metrics to compare the two approaches.

JH
fpd164  [Member]
4/16/2009 10:46:31 AM
is that Justin Timberlake in the last pic???????
JK!
looks great
Eric802  [Team Member]
4/16/2009 12:35:59 PM
Nice write-up. Seems like you've read up on the various methods already, so you're already aware of the flatter trajectory you get from the 50 yard zero, but I'll be interested to see the data you get with more shooting with the 25 meter zero.
USMC-Helo  [Member]
4/16/2009 1:33:04 PM
Well, a flatter trajectory up to 250-275 yards. After that, it falls off more rapidly than a 25 yard zero. It depends on the trade off you want to make for the distances you shoot, if you shoot at ranges less than 300yards, yea 50 yard zero seems to make more sense to me. NOT sure if you want to shoot out to 500 yards. As well, if you have sights with elevation correction, which zero is better?
QuicksilverJPR  [Team Member]
4/16/2009 1:57:47 PM
Originally Posted By USMC-Helo:
Well, a flatter trajectory up to 250-275 yards. After that, it falls off more rapidly than a 25 yard zero. It depends on the trade off you want to make for the distances you shoot, if you shoot at ranges less than 300yards, yea 50 yard zero seems to make more sense to me. NOT sure if you want to shoot out to 500 yards. As well, if you have sights with elevation correction, which zero is better?


That's why "they" now use SPR/DMR type rifles (in reference to the 500 yard shooting stuff)

Seriously, That's a different game there. If you're shooting at 500, usually you're scoped and zeroed for that distance...

m1garand__man  [Member]
4/16/2009 2:19:02 PM
thats interesting to set the m4 sight to Z to zero. I wonder why the army TM says to leave it at the 6/3 mark for a 300m zero. that would seem to mean it would then have to hit too high at 300m.
Molon  [Team Member]
4/16/2009 2:37:13 PM
Originally Posted By m1garand__man:
thats interesting to set the m4 sight to Z to zero. I wonder why the army TM says to leave it at the 6/3 mark for a 300m zero.


Two different animals. The military uses 14.5" barrels on the M4. The majority of civilian M4 immitations have 16" barrels resulting in a difference in muzzle velocities.

MOS2111  [Team Member]
4/16/2009 3:12:38 PM
1. Did you mechanically zero the FSP? (make the FSP even to the flat portion btwn the front site ears?)
2. You are zeroing a 16 inch carbine, using the z mark on an A2 target.... You need to get the m4 target.

I use the 25/300 yd zero on all my irons and a flat 50 on all my red dots. I am better at shooting distance with Irons, so when a long shot comes up, dial it and send it.


ETA-
3. There is a 36 m/yd? target. I have it and will willing send you a 100% scale in PDF if you agree to host it.
jimmyhots  [Member]
4/16/2009 6:51:39 PM
Originally Posted By MOS2111:
1. Did you mechanically zero the FSP? (make the FSP even to the flat portion btwn the front site ears?)
2. You are zeroing a 16 inch carbine, using the z mark on an A2 target.... You need to get the m4 target.

I use the 25/300 yd zero on all my irons and a flat 50 on all my red dots. I am better at shooting distance with Irons, so when a long shot comes up, dial it and send it.


ETA-
3. There is a 36 m/yd? target. I have it and will willing send you a 100% scale in PDF if you agree to host it.


Hmm I don't think I've seen the M4 target. Since the A2 target is for a 20" rifle and the M4 target is for a 16", I'm guessing the main difference in the targets is the size of the grid squares used to determine the number of clicks to center? I did notice when zeroing that the number of clicks suggested by the target was maybe a little off. This could be explained by the difference in front-rear sight distance between 20" & 16" barrels, and corresponding MOA differences in the adjustments.

Sounds like the M4 target is meant to be used at 36 meters (i.e. first cross-over), with rear elevation bottomed-out at 6/3?

I'd be happy to host it if you want to send, assuming it's legal to host (i.e., no copyright infringement).

Jimmy
locke12  [Member]
4/16/2009 7:13:02 PM
Very nice article, Jimmy. You did an excellent job of explaining the sometimes cryptic BZ. Thank you, and I am looking forward to your updates. I will refer back to your article if I EVER GET MY NEW BARREL!!!!!
Muttt  [Member]
4/16/2009 7:22:45 PM
Very nicely done, and very informative. Unfortunately, the rear sights with elevation adjustment are just way to high for me to use as a BUIS. So, I just go with a simpler BUIS that only adjusts for windage. So, I really do prefer the 50 / 200 sight in proceedure for two (very important to me) reasons. 1 my sights don't allow for elevation at the rear sight 2 both the locall ranges that I have access to only go out to the 200 yard range. So, for now, I am just gonna stick with the 50 /200. But, I would really love to get access to a 500 yard range again. I'd love to try some other longer range stuff. Just don't have the access. Anyhow ....... good work. Obviously done for the betterment of your fellow man/shooter.
jblomenberg16  [Member]
4/16/2009 7:36:09 PM
Very nice write up. I've been experimenting on the sight in and trajectories of both of my 16" AR's - one a HBAR middy and the other a 16" M4 carbine clone (S&W M&P15, so in essence very similar to what you sighted in for the write up). My ammo of choice is Federal A/E M193 as well.

Both have been initially sighted in using the 25m sight in, and will shoot comparable groups at 25m (usually within a 1" circle or so if I do my part). The Middy has the Matech 600m BUIS and standard A2 front sight, and the M4 has a YHM flip up rear BUIS (dual appetures, but no elevation adjustment) and a MI flip up front sight.

I shot the middy at about 125m this weekend and was about 7" high on the target with the Middy and Matech at the 300m setting, which is in the ballpark of where it should be, but a little high from the trajectory you've shown. I had similar results with that rifle and the 6x scope that is on it, which I also initially sighted in at 25m.

I bought the Matech used, so I need to read up a bit on the sight in setting, but I was using the 300m mark as a guide. I'd like to try the 50m sight in and see what the difference is at the various distances. Looking forward to results if you do the same. Most of my shooting is well inside 200m, and usually < 100m. So, I'd like to get an optimal sight in for those ranges.

Again, very good write up!
Skraeling  [Member]
4/16/2009 10:57:39 PM
Excellent writeup, I still need to fix my point of aim and left right adjustment :\

jimmyhots  [Member]
4/19/2009 1:45:02 PM
FYI I made updates to the article to address the difference between the M4 & A2 zeroing targets, and how this difference affected my zeroing procedure. Thanks to MOS2111 for pointing out the existence of the M4 target.

JH
jimmyhots  [Member]
4/19/2009 2:12:40 PM
Originally Posted By m1garand__man:
thats interesting to set the m4 sight to Z to zero. I wonder why the army TM says to leave it at the 6/3 mark for a 300m zero. that would seem to mean it would then have to hit too high at 300m.


The manual says to raise the rear elevation up one click (two clicks for rifles having half-clicks) from bottom during the zeroing procedure, and then lower back to bottom when complete to obtain the 300 meter zero. The reason for this is explained in my article, but in short it's because the first cross-over occurs at a range past 25 m (where the target is), so the rifle is going to strike low at 25 meters. Raising the rear elevation one click (or two half-clicks) raises the strike of the rifle (in theory) just enough to give a true line-of-sight strike at 25 meters. Once zeroing is complete, the rear sight is brought back to bottom, thus moving the first cross-over from 25 meters out to about 37 meters (or 30 meters for 2.6-inch deviation sights), and second cross-over at the prescribed 300 meters (sight-in distance).

JH
STRIKE504  [Member]
9/14/2009 9:24:40 AM
Originally Posted By jblomenberg16:
Very nice write up. I've been experimenting on the sight in and trajectories of both of my 16" AR's - one a HBAR middy and the other a 16" M4 carbine clone (S&W M&P15, so in essence very similar to what you sighted in for the write up). My ammo of choice is Federal A/E M193 as well.

Both have been initially sighted in using the 25m sight in, and will shoot comparable groups at 25m (usually within a 1" circle or so if I do my part). The Middy has the Matech 600m BUIS and standard A2 front sight, and the M4 has a YHM flip up rear BUIS (dual appetures, but no elevation adjustment) and a MI flip up front sight.

I shot the middy at about 125m this weekend and was about 7" high on the target with the Middy and Matech at the 300m setting, which is in the ballpark of where it should be, but a little high from the trajectory you've shown. I had similar results with that rifle and the 6x scope that is on it, which I also initially sighted in at 25m.

I bought the Matech used, so I need to read up a bit on the sight in setting, but I was using the 300m mark as a guide. I'd like to try the 50m sight in and see what the difference is at the various distances. Looking forward to results if you do the same. Most of my shooting is well inside 200m, and usually < 100m. So, I'd like to get an optimal sight in for those ranges.

Again, very good write up!


Using the 25m zero, I was always told you'd be approx. 5" high @ 100m and 11" low @ 300m. You always had to aim at the burm at 100m and the neckline at 300m at the pop up range. (using 14.5" m4, CCO)
MikefromTX  [Member]
9/14/2009 2:39:59 PM
Nice detailed write-up. I'm confused, though - you started out raising the front sight 2 clicks, then lowered it two clicks (one after the second group and another one after the third group). So ... you basically put it back where it was when you started. Why did your POI change?

One other thing ... I'm glad you mentioned that bullets don't take wing and start rising after leaving the muzzle. that might be better illustrated if you made the little "barrel" icon at the left edge of your graph point upward in the same plane as your bullet path, instead of being horizontal.

.
.
lsujim  [Team Member]
9/14/2009 2:55:42 PM
Nice write up. Thank you.
Postal0311  [Life Member]
9/14/2009 3:24:49 PM
Ok, here is some info:

USMC prefers a 36/300 zero (leave it on 8/3 or 6/3). Army is one that uses the 25m zero.

With the 25m zero, one uses 8/3+1 or 6/3+2 (Z marking) on a RIFLE. Due to the different ballistics of the M4, you leave it on 8/3 or 6/3 for the carbine.

There are different M4 and M16 Army 25m bzo targets. The differences are due to the sight radius changing the adjustment amounts. The current Army 25m target is slightly off causing solders to over correct.
The USAMU is working on a new BZO target.

The AMU recommends that the impacts should be in the bottom half of the circle when BZOing at 25 meters. This will effect POI slightly, helping lower the 7-9 inch high point of the trajectory at about 175 yards.

As for the 50/200 zero, many fail to realize that with most ammo, and most AR setups a 50 yard zero will not equal a 200m zero. However it will still be close enough for the desired effect. Some of the proponents of the 50/200 zero claim that it is much flatter shooting then the zero really is, however if you look at the numbers and shoot targets at the distances, its still a good set up.
bigmoney327  [Member]
9/14/2009 3:33:07 PM
awesome writeup. well done.
eightring  [Member]
9/15/2009 12:09:12 PM
All this good work has me thinking about rifle sighting.

I did the calculations for 200M zero and 300M zero.


As posted, the 200M zero gives a much flatter trajectory for short ranges.

There is a problem with the 200M zero IMO.
If you have a 200M zero and want to shoot beyond 200M, you have to hold over.
But, you really can't see the target when you hold over because the muzzle is in the way.

With a 300M zero, you have to hold under at shorter ranges, but you can shoot to 300M
without having to hold over.
Eric802  [Team Member]
9/15/2009 2:15:23 PM
Originally Posted By eightring:
As posted, the 200M zero gives a much flatter trajectory for short ranges.

There is a problem with the 200M zero IMO.
If you have a 200M zero and want to shoot beyond 200M, you have to hold over.
But, you really can't see the target when you hold over because the muzzle is in the way.

With a 300M zero, you have to hold under at shorter ranges, but you can shoot to 300M
without having to hold over.


And with the 300M zero, you have to hold over to shoot farther than that. It's true with ANY zero - if you're shooting farther than you have it zeroed, you have to hold over...OR...dial up the rear sight. That's why it's adjustable, after all. Bottom line is, for the most part any shooting folks here are doing past 200 yards will either be with optics, or for a specific purpose - like highpower competition - where you'll be using a different zero anyway. And for shooting 0-200 yards, the 50 yard zero is a vast improvement over the 300M zero, because you're so close to the line of sight the whole way out.
eightring  [Member]
9/15/2009 3:24:56 PM
Originally Posted By Eric802:

And with the 300M zero, you have to hold over to shoot farther than that. It's true with ANY zero - if you're shooting farther than you have it zeroed, you have to hold over...OR...dial up the rear sight. That's why it's adjustable, after all. Bottom line is, for the most part any shooting folks here are doing past 200 yards will either be with optics, or for a specific purpose - like highpower competition - where you'll be using a different zero anyway. And for shooting 0-200 yards, the 50 yard zero is a vast improvement over the 300M zero, because you're so close to the line of sight the whole way out.


There is no doubt that a 200M zero is far better for shooting 0-200M.
(It is also true that a 100M zero is even better for shooting 0-100M.)

But, I am sort of worried about limiting my ability to engage targets at greater distances.
At the range, we would practice with teams attacking pop-up targets at
100yd, 200yd, and 300yd.

It worries me to have a "short zero" and not be able to engage targets out to 300yd.
Beyond 300yd, I would not consider an M4 to be particularly effective anyway.



jimmyhots  [Member]
10/7/2009 12:16:16 AM
Originally Posted By MikefromTX:
Nice detailed write-up. I'm confused, though - you started out raising the front sight 2 clicks, then lowered it two clicks (one after the second group and another one after the third group). So ... you basically put it back where it was when you started. Why did your POI change?

Good point, you read the article in detail I see he he. I wondered the same thing, and I don't really have a good answer. All I can say is that @ 25 meters the silhouette looks pretty small using iron sights and I suspect that I was being a bit inconsistent with my sight picture. At distance the silhouette yields very little side-to-side play, but vertically there is more "play" in the sight picture, making it more of a challenge to obtain consistent groups.


One other thing ... I'm glad you mentioned that bullets don't take wing and start rising after leaving the muzzle. that might be better illustrated if you made the little "barrel" icon at the left edge of your graph point upward in the same plane as your bullet path, instead of being horizontal.

Yes I agree but the software I used doesn't allow for that :-)
MOS2111  [Team Member]
10/7/2009 8:54:26 AM
check your thread on m4, I added a very relevant link.
R0N  [Team Member]
10/7/2009 9:16:16 AM
Per Marine Corps ART -4 (Annual Rifle Training-4, rifle zeroing) we don't "BZO" at 25 meters, the zero is conducted at 36 yards or 32-33 meters or at either 200 meters or 300 meters when using iron sighted weapons. An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.

When using an RCO, the sight is zeroed viced BZOd and the intial setting should be done at the same distance as iron sights and confirmed at 100 meters.
MOS2111  [Team Member]
10/7/2009 11:24:24 AM
Originally Posted By R0N:
Per Marine Corps ART -4 (Annual Rifle Training-4, rifle zeroing) we don't "BZO" at 25 meters, the zero is conducted at 36 yards or 32-33 meters or at either 200 meters or 300 meters when using iron sighted weapons. An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.

When using an RCO, the sight is zeroed viced BZOd and the intial setting should be done at the same distance as iron sights and confirmed at 100 meters.


How is it that I distinctly remember using this 25 yd bzo with the A2 in boot, MCT, and at the range in my unit? This was 5+ years ago. Has this process changed recently. I understand that the 20 inch barrel needs to be zeroed "idealy" at 50.....
Postal0311  [Life Member]
10/7/2009 11:30:35 AM
As I said before:

36 yards on the 300m setting for the Rifle
Or 25m 8/3+1 or 25m with 6/3+2 (z setting) for zeroing a rifle.

Due to the ballistics of the M4, leave it on 8/3 or 6/3 at 25meters.

Every time we did a BZO while I was in, it was at 36 yards. USMC SOP is 36 yards, Army 25m. I never heard of the 25m BZO until I talked to some Army folks. MOS2211 you may be mistaken, or perhaps your instructors were mistaken, or hopefully you were just using the 25m version of the zeroing procedure.

As for the 50m zero, it is not an official mil zero. Some units may choose to employ this zero, but it is not in military doctrine. Individuals should look at the ballistics of each zero and decide which is best for them.
SSeric02  [Team Member]
10/7/2009 11:53:24 AM
Originally Posted By MOS2111:
Originally Posted By R0N:
Per Marine Corps ART -4 (Annual Rifle Training-4, rifle zeroing) we don't "BZO" at 25 meters, the zero is conducted at 36 yards or 32-33 meters or at either 200 meters or 300 meters when using iron sighted weapons. An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.

When using an RCO, the sight is zeroed viced BZOd and the intial setting should be done at the same distance as iron sights and confirmed at 100 meters.


How is it that I distinctly remember using this 25 yd bzo with the A2 in boot, MCT, and at the range in my unit? This was 5+ years ago. Has this process changed recently. I understand that the 20 inch barrel needs to be zeroed "idealy" at 50.....


IIRC, the original M16A2 operator's manual used the 25m zero. We (the USMC) changed to the 36yd zero in 98/99 based on the reasons RON gave and this change was documented in MCRP 3-1A Rifle Marksmanship. The Army continues to use the 25m method.
MOS2111  [Team Member]
10/7/2009 12:45:23 PM
Just to add
http://www.usaac.army.mil/amu/ServiceRifle/M16-M4%20data.pdf
Molon  [Team Member]
10/7/2009 10:20:28 PM
Originally Posted By R0N:

An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.



Yet another Internet myth that just won’t die and one that is usually perpetuated by those who fail to understand gyroscopic stability factors. In order for a bullet to be stable in flight, it must have a gyroscopic stability factor greater than 1 as it exits the muzzle of the barrel. “Generally speaking, the optimum range of the gyroscopic stability factor for accuracy is about 1.5 – 2.0.”* The gyroscopic stability factor of M855 as it exits the barrel of a 20” M16A2 is approximately 2.13; clearly making it stable as it exits the muzzle.


*NRA Firearms Fact Book, page 236
RRA223  [Team Member]
10/8/2009 2:57:47 AM
OP

Because of the 300 meter rifle sights, then this is fine to do. My rifles don't have the M2 sights so my sights are zeroed at 200 meters.
The rifle with a scope has a 100 yard zero.

It really don't matter what zero I use, as long as you know what YOUR zero is.

Here is a chart I use: 200 meter zero.........218 yards is 200 meters......................

Name: 5.56 NATO 20 inch RRA barrel
Ballistic Coeff: 0.259
Bullet Weight: 55
Velocity: 3200
Target Distance: 218
Scope Height: 2.600
Temperature: 70
Altitude: 500

Ballistic Data
~~~~~~~~~~~~~~~
Range Elevation Velocity Energy ETA Drop Max Y 10mph Wind Deflect
0 yds -2.60 in 3200 fps 1250 fpe 0.000 sec 0.00 in -2.60 in 0.00 in
25 yds -1.30 in 3106 fps 1178 fpe 0.024 sec 0.11 in -1.01 in 0.07 in
50 yds -0.23 in 3015 fps 1110 fpe 0.048 sec 0.44 in -0.93 in 0.24 in
75 yds 0.61 in 2925 fps 1045 fpe 0.073 sec 1.01 in -0.78 in 0.55 in
100 yds 1.19 in 2837 fps 983 fpe 0.099 sec 1.84 in -0.56 in 1.01 in
125 yds 1.50 in 2751 fps 924 fpe 0.126 sec 2.93 in -0.26 in 1.62 in
150 yds 1.52 in 2667 fps 868 fpe 0.154 sec 4.32 in 0.12 in 2.38 in
175 yds 1.24 in 2584 fps 815 fpe 0.183 sec 6.01 in 0.58 in 3.29 in
200 yds 0.65 in 2502 fps 765 fpe 0.212 sec 8.01 in 1.15 in 4.33 in
225 yds -0.30 in 2422 fps 717 fpe 0.242 sec 10.36 in 1.82 in 5.55 in
250 yds -1.62 in 2344 fps 671 fpe 0.274 sec 13.09 in 2.61 in 6.96 in
275 yds -3.35 in 2267 fps 628 fpe 0.307 sec 16.23 in 3.53 in 8.58 in
300 yds -5.50 in 2191 fps 586 fpe 0.340 sec 19.79 in 4.59 in 10.41 in
325 yds -8.11 in 2117 fps 547 fpe 0.375 sec 23.80 in 5.81 in 12.43 in
350 yds -11.17 in 2044 fps 510 fpe 0.411 sec 28.28 in 7.18 in 14.63 in
375 yds -14.76 in 1973 fps 475 fpe 0.449 sec 33.27 in 8.74 in 17.06 in
400 yds -18.84 in 1903 fps 442 fpe 0.487 sec 38.75 in 10.47 in 19.65 in
425 yds -23.60 in 1835 fps 411 fpe 0.527 sec 44.93 in 12.45 in 22.59 in
450 yds -29.08 in 1768 fps 382 fpe 0.569 sec 51.81 in 14.68 in 25.85 in
475 yds -35.29 in 1704 fps 355 fpe 0.612 sec 59.43 in 17.19 in 29.41 in
500 yds -42.26 in 1642 fps 329 fpe 0.658 sec 67.80 in 19.97 in 33.23 in
525 yds -49.98 in 1581 fps 305 fpe 0.704 sec 76.93 in 23.05 in 37.29 in
550 yds -58.47 in 1522 fps 283 fpe 0.752 sec 86.83 in 26.44 in 41.59 in
575 yds -68.01 in 1465 fps 262 fpe 0.802 sec 97.77 in 30.22 in 46.27 in
600 yds -78.63 in 1411 fps 243 fpe 0.854 sec 109.81 in 34.41 in 51.32 in
625 yds -90.49 in 1360 fps 226 fpe 0.909 sec 123.08 in 39.07 in 56.77 in
650 yds -103.57 in 1312 fps 210 fpe 0.965 sec 137.56 in 44.20 in 62.56 in
675 yds -117.83 in 1266 fps 196 fpe 1.023 sec 153.23 in 49.81 in 68.65 in
700 yds -133.56 in 1224 fps 183 fpe 1.083 sec 170.36 in 55.96 in 75.11 in
725 yds -150.88 in 1185 fps 171 fpe 1.145 sec 189.09 in 62.72 in 81.96 in
750 yds -169.78 in 1149 fps 161 fpe 1.210 sec 209.39 in 70.07 in 89.14 in
775 yds -190.40 in 1117 fps 152 fpe 1.276 sec 231.42 in 78.07 in 96.67 in
800 yds -212.78 in 1088 fps 145 fpe 1.344 sec 255.21 in 86.73 in 104.51 in
R0N  [Team Member]
10/8/2009 5:08:30 AM
Originally Posted By Molon:
Originally Posted By R0N:

An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.



Yet another Internet myth that just won’t die and one that is usually perpetuated by those who fail to understand gyroscopic stability factors. In order for a bullet to be stable in flight, it must have a gyroscopic stability factor greater than 1 as it exits the muzzle of the barrel. “Generally speaking, the optimum range of the gyroscopic stability factor for accuracy is about 1.5 – 2.0.”* The gyroscopic stability factor of M855 as it exits the barrel of a 20” M16A2 is approximately 2.13; clearly making it stable as it exits the muzzle.


*NRA Firearms Fact Book, page 236


Two points, first the Marine Corps cited this based on input from Aberdeen proving ground as to one of the reasons that a zero greater than 25ms was ideal. Second I would have to say the NRA is wrong on this one, since the Marine Corps has high speed video showing the round porpoising in flight that I have seen before, in it there are white and black stripped projos and you see them going above and below the line of flight.
Shung  [Member]
10/8/2009 6:37:59 AM
great page ! added to favourite ! thx a lot !
Molon  [Team Member]
10/8/2009 9:40:58 AM
Originally Posted By R0N:
Originally Posted By Molon:
Originally Posted By R0N:

An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.



Yet another Internet myth that just won’t die and one that is usually perpetuated by those who fail to understand gyroscopic stability factors. In order for a bullet to be stable in flight, it must have a gyroscopic stability factor greater than 1 as it exits the muzzle of the barrel. “Generally speaking, the optimum range of the gyroscopic stability factor for accuracy is about 1.5 – 2.0.”* The gyroscopic stability factor of M855 as it exits the barrel of a 20” M16A2 is approximately 2.13; clearly making it stable as it exits the muzzle.


*NRA Firearms Fact Book, page 236


Two points, first the Marine Corps cited this based on input from Aberdeen proving ground as to one of the reasons that a zero greater than 25ms was ideal. Second I would have to say the NRA is wrong on this one, since the Marine Corps has high speed video showing the round porpoising in flight that I have seen before, in it there are white and black stripped projos and you see them going above and below the line of flight.


The study and video that you are referring to are about PRECESSION which is different from GYROSCOPIC STABILITY and as I stated earlier the myth is propagated by those who fail to understand the difference between the two.
R0N  [Team Member]
10/8/2009 10:01:29 AM
Okay, so it fully not stablized because of precsssion, it doesn't change the reasons behind why the Marine Corps didn't want to do a 25M zero.
Molon  [Team Member]
10/8/2009 10:16:01 AM
Originally Posted By R0N:
Okay, so it fully not stablized because of precsssion, it doesn't change the reasons behind why the Marine Corps didn't want to do a 25M zero.


Once again you confuse PRECESSION with STABILITY. A bullet that has a gyroscopic stability factor of 2.13 and that is exibiting precession is stable and is at no risk of becoming unstable. I've seen studies that indicate that the preccession of M855 doesn't actually diminish until closer to 100 meters. By your own failed logic, the Marines 36 yard zero is useless because the bullet is still exibiting precession at that distance. By your own failed logic all zeroing with M855 should be conducted at a distance of at least 100 meters.

All theory aside, anyone who posses the basic skills of marksmanship fundamentals can disprove your theory of "instability" at 25 meters. I have absolutely no problem, shooting 10-shot group after 10-shot group of M855 that go into one small ragged hole at a distance of only 23 meters; which of course would be impossible to do if the bullets were not actually stable at that distance
R0N  [Team Member]
10/8/2009 10:36:23 AM
How big of a ragid hole are we talking about? Since you are dealing with angles, I would argue you may not even see the effect.

However, it doesn't change that it is one of the reason cited by the Marines that the Marines didn't use a 25m zero.
BamaInArk  [Team Member]
10/8/2009 2:29:58 PM
Originally Posted By Molon:
Originally Posted By R0N:

An additional factor is that the M855 round takes a nominal 27 meters to stablize, so zeros conducted beneath that range are considered suspect.



Yet another Internet myth that just won’t die and one that is usually perpetuated by those who fail to understand gyroscopic stability factors. In order for a bullet to be stable in flight, it must have a gyroscopic stability factor greater than 1 as it exits the muzzle of the barrel. “Generally speaking, the optimum range of the gyroscopic stability factor for accuracy is about 1.5 – 2.0.”* The gyroscopic stability factor of M855 as it exits the barrel of a 20” M16A2 is approximately 2.13; clearly making it stable as it exits the muzzle.


*NRA Firearms Fact Book, page 236


Now this has me wondering....then just what is the fleet yaw issue we've been seeing so much of lately? Isn't that instability out of the barrel?

Ah I see now...
Yaw is not instability; it occurs naturally in all spin-stabilized projectiles. However, bullet yaw is not constant and rifle bullets
display three regions of significantly different yaw (see Figure 5). Close to the muzzle, the bullet’s yaw cycles rapidly, with large changes of angle
in very short distances (several degrees within 1-2 meters range). Eventually, the yaw dampens out and the
bullet travels at a more-or-less constant yaw angle for the majority of its effective range. Then, as the bullet slows, it begins to yaw
at greater and greater angles, until it ultimately destabilizes.
Winn  [Team Member]
10/20/2009 8:07:46 PM

.

jimmyhots  [Member]
11/3/2009 11:16:26 PM
Originally Posted By MOS2111:
check your thread on m4, I added a very relevant link.


Thanks for the info, some good stuff there. By the way I haven't looked at this thread in a while, hence the delayed response.
Frozenbones  [Team Member]
11/4/2009 3:48:05 AM
Very nice write up.
rod556  [Member]
11/4/2009 6:33:05 AM
Nice write-up! Thank you for contributing your time and effort to help the AR community. Too bad that so many people spend their time arguing. I would suggest that their time and effort would be better spent at the range, dialing-in whatever zero they prefer.
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