Why Army and Marines have differnt zero standards?

[elephant]

I got interested in this a few days ago when I was wondering what the best method of zeroing a standard 16" OAL 556, I had always been told to zero optics and sights to 100 yards. I asked some guys at my LGS and one guy said 25-300 meter and another guy said 36-300 yard. I then learned that the Army teaches meters and the Marines teach yards. Then they went into talking about astrophysics, ballistics, quantum mechanics and started talking about BZO and how zeroing at 25 meter, 36 yard, and 50 yard is only to get you on paper and close to where you should be shooting at 300 meters, 300 yards, and 200 yards. I didn't understand a word of it yet I nodded and told them it made perfect sense and thanked them.

For a civilian with a 16" OAL 556, what is the best approach to zeroing BUIS, red dot & Peq-15? All the same or slightly different?

[tigershilone]

For zeroing, Stickies have this covered:

https://www.m4carbine.net/showthread...d-Trajectories
https://www.m4carbine.net/showthread...M855-and-Mk262
https://www.m4carbine.net/showthread...100-Meter-Zero

As to why army and marines are different in teaching, I thought they both used meters, something to do with artillery ranging standards that drifted over to everything else (MILS ?).

[MA2_Navy_Veteran]

I'll just leave this here...

[elephant]

looks like the 200 yard zero is best all around. 2.5 inch combat effective zone.

[MegademiC]

Another freat thread:
https://www.m4carbine.net/showthread...M855-and-Mk262

[lysander]

I don't know where you got the Marine Corps only uses yards. According to MCRP 3-01A, Rifle Marksmanship (USMC), Chapter 8, the pre-zero range for the Back Up Iron Sight (BUIS) is given as "33 meter/36 yards" (page 8-10). This is most likely due to some of the older range complexes being from the pre-metric military era. However, this publication further states the final (official) zero shall be conducted at "300 meters/yards", the practical difference between the two, 25.7 meters or 28.1 yards, depending on which way you go, has little impact on combat effectiveness.

As to why they zero differently is due to the differences between the two services qualify. Since the USMC still uses the Known Distance (KD) range for qualification, the rifle is zeroed at 300 meters (or yards depending on where the range's firing point are actually located) to align with the 300 meter/yard prone rapid stage of qualification, which is considered "Battle Sight Zero". Moving the sights to the 200 mark for the short range stage and going up to the 600 mark for the long range stage.

The Army doesn't like to mess with the sights, and so uses a 25 meter zero range, with the sight set at special places depending on weapon type, then never touches the sights again. Since the Army qualification is at "E" and "F"-type silhouettes that pop-up and a hits are scored as either "hit" or "miss", being a foot from your point of aim low or high at 300 meters is not that big a deal (unless you have lousy fundamentals).

The trajectory of a bullet fired passed through the line of sight twice, once at short range as it travels upward and once when it passes through the zero range. For any given muzzle velocity and sight height, this two ranges are fixed. With M855, fired from a 20 inch barrel will cross the line of sight at 33 meters and 300 meters, which is how the USMC manual reads. Per the Army manual, you adjust the rear sight of an M4 to 3/6 and use the small aperture and zero at 25 meters then switch to the large aperture, which theoretically gives you a zero at 300 meters.

Why the Army goes through this complex drill of sight adjustment is due to the fact that the Army has long used the "1000 inch range" (25 meters) for qualification for machine guns, and they have a lot of them next to longer range complexes, and they never felt the need to move the target stands back 11 meters...

To better understand each service's qualification methods, rather than listen to "some guy", read the actual manuals, they can be found on-line for free

ARMY: FM 3-22.9 - Rifle Marksmanship M16-M4 Series Weapons (Aug 2008, w/ chg 1)
USMC: MCRP 3-01A - Rifle Marksmanship (11 Oct 2012)

As to how you should zero, zero at the most likely range you will be shooting.

[CPM]

I zero at 50 and have no issue hitting 10” steel plates at 300 yards.

[Jonnyt16]

I'll just leave this here...

WTF?? With a 100 yard zero your POI will be low at 0-50 yards, NOT high like Haley demonstrated above. Not really sure how he came up with that. Really strange.

[vicious_cb]

Maybe people should stop worrying about what the military is using and instead pick the zero that is appropriate for their optic and typical engagement range.

[RHINOWSO]

Maybe people should stop worrying about what the military is using and instead pick the zero that is appropriate for their optic and typical engagement range.

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I zero at 100, because that is my max probably civie engagement range.

Inside of that, an inch low is still a hit. In general I prefer low hits to high hits.

I asked some guys at my LGS...

First mistake...