Zero Range for a 10.5 inch upper

[Swank]

I need the bullet data on the M855, with a 10.5in upper(Colt and Bushmaster), with a EOTECH on it. Trying to find out what the zero range needs to be.

Guys, this is a short fuse request from a friend of mine in DSS. They normally zero for 100m.

18B's, let's see what you got.

[The Reaper]

Guys, this is a short fuse request from a friend of mine in DSS. They normally zero for 100m.

18B's, let's see what you got.


I hate to sound like a smart ass, but it depends on how far they are expecting to engage targets.

TR

[Swank]

100m.

[jatx]

I went through this exercise myself recently.

First off, it is hard to say precisely without knowing what weight bullets they will be launching, but I assume they will be using 75 or 77 gr. rounds. Using 75 gr. TAP, POI is within roughly 1.25" of POA all the way out to 150 yards using a 100 yard zero. However, drop is about 4" at 200 yards and about 14" at 300. I hope that helps.

[optactical]

1. Shoot irons for a 25m-300m zero. Point of aim at 25m is point of impact at 25m and 300m

2. Mount red dot optic of choice.

3. Co-witness red dot to irons sights.

4. Confirm red dot zero using ammo.

5. Mount IR Laser sighting device (PAQ4, PEQ2, PEQ15).

6. Put on NVG, set red dot to NVG setting.

7. Co-Witness red dot with IR Laser at anywhere from 100-300m depending on range you have, 300 is most preferred (using NVG looking through sight).

8. Confirm IR Laser sighting device on paper if you feel it is necessary with the 25m target using ammo.


If you do this right and you don't shoot like a shotgun on crack, you can do this with about 20 rounds per man.

Biggest problems ever seen were operator headspace and timing, ensure all sights are tightened down (#1 problem!!), ensure you know what each click on whatever sight you are using will move that sight at 25m. Know that 1 moa at 25m is a 1/4 inch, therefore 1/2 moa adjustments on your sight will move the bullet 1/8 of an inch at 25m.

Shoot 3-5 round groups, I prefer 5, the Army says 3, I say FTA and do it the way I know works, but that's just me, the bigger the group, the better the shift. Measure from the center of the group for moving the impact.

10.5's that are brand new shoot rather well at the range on the first day, just be sure to confirm those zeros ever few ranges, the sights can get quirky after a couple thousand rounds through them, I have seen up to 4 or 5 moa shifts from one day to the next on them, it was usually an EO Techs Fault though, the irons held true for the most part.

HTH

[The Reaper]

100m.

Then why not zero at 100m.? It is not like the shorties are going to be useful at extended ranges much beyond that.

If you zero at a shorter range, you will be low at 100, longer range and you will be high at 100.

The bullet flies in an arc, like a rainbow. The 1.4" of the sight plane above the bore on the M-16/AR-15 series weapons exacerbates this effect. It crosses the sight line twice on the way to the zero target, once on the way up and once on the way down. That is how a 25m. zero puts the bullet on the target at 300m, and can hit all of the targets on the qualification range from 25 to 300m.

For this application, unless they are shooting almost exclusively closer, or further, I would leave it at 100, and shoot the intermediate distances to determine the holdover (or under).

Just my .02, YMMV.

TR

[optactical]

The problem with zeroing at 100m with this barrel and optic is your group is relatively large. I always liked 25m/300m for general applications since I know where a 25m zeroed barrel will hit at 10m, 15m etc for CQB. Also, like you stated it covers the spectrum from 0-300 if aiming center mass.

If he wants to have a 100m zero, have him shoot a 25m zero first, this will get him on target, then shoot a 100m target and adjust down and for windage as necessary.

[Swank]

Yep, I agree with that. DoS range master doesn't and wants to zero closer. This basically is two BFOC'ers (I can't rember what that stands for, basically a DoS range guy) trying to decide whether to zero these guys with 10.5 inch barrels at 50 or 75. The sr guy is saying 50. Other guy says 75. And one lonely former bat boy SOTIC grad who just wants to shoot his gun.

[Lmmsoat]

I agree with Rreaper. Zero the gun for 100m and get dope for 150-300 (300 is optamistic for a 10.5"). Most guys I know (including myself) use the 100m Zero for their shorties. Just don't forget to aim a little high at cqb distances.

BTW what is everyones take on the 200m zero for M-4 length? I've been using it for several years now. I find it works great for 14.5" uppers.

[Swank]

It has been decided. Yea, and the thunder clapped and the clouds parted, and 50m was handed down from on high. And there was much rejoicing. And cake.

[Peregrino]

Just to add to the confusion: http://www.professionalsoldiers.com/forums/showthread.php?t=5370&highlight=Battle+sight

This is a thread that explains all of the variables for BSZs. (Thought I remembered this conversation at some point in the distant past. Love that search button! :p )

[Blitzzz (RIP)]

if you zero at 100 meters then the following:

M-193 ball = 4 inch target area out to 150 meters.

M-855 ball =4.2 inch target area out to 150 meters.

Added Info:
also if you zero the M193 ball @ 250ms you have +9.9 inch at 200ms, -15.1 at 300.

and for the M855 ball with 300 meter zero, = a +12.6 inches @ 150+
I'd do the 100 meter zero
Blitz