Zeroing/iron sights on Bushmaster XM15 ES2S

[Lugnut]

My AR15 has A3 sights so one click (elevation) is 1/2MOA (which I think different from other AR15s). I finally think I get the MOA stuff. But what I'm still baffled on (and I've searched and read a lot) is how to actually use the elevations at different distances. (I haven't done anything beyond 50 yds yet- I'm still trying to understand all this though!

1) First- can the normal aperture rear sight(smaller hole) be used interchangably with the short aperture (big hole) at close ranges? Or does it effect the POI?

I assume I should Zero the gun at the 'z' mark at 25yds (per directions)? So that the POI is just level with the top of the front sight? Why at 'z'?

2) My elevation knob has a 6/3 mark, then 2 notches/click 'up' has a 'z', then 2 clicks up form there it has a '4', then 8 clicks up from there is has a '5', then 11 clicks from there is at back at the 6/3 mark again. I know the numbers are "hundreds" of yards but if each click is 1/2 MOA does this mean for example that the 223 drops 8 MOA between 4 and 5 hundred yards? With my calculation that would be 16 inches (8 clicks-1/2MOA each, with 1 MOA=4" @ 400yds)??? Doesn't seem right to me.

Maybe I'm making this much more complicated that I need to but I feel a little slow with all this sighting stuff!

 

[Big Daddy 45acp]

http://fsguns.com/ibsz.html

Check out this link. I sent this info to Carl a while back and he posted it on his site.

Hope this helps!

 

[crak]

This might clear up some of the confusion:

When the bullet leaves the rifle barrel, it's still travelling up. For example, if I lined up two targets at 25m and 200m and shot them with my 7.62 NATO, the bullet is travelling up as it hits the 25m target, reaches the top of its climb somewhere in the middle, and hits the 200m target on the way down in about the same spot. The details of this are different from one load to another, but the idea's the same.

After shooting 25m AQTs, I didn't have to change anything when I went to a 200m offhand match. I was worried about not being zeroed for the match because I didn't have anywhere to shoot the real distance, but the director at Reading explained that if it wasn't exact, it'd be close enough to fix after looking at the first couple of shots through the scope. It worked out perfectly.

Rifles are typically set to a battle sight zero (BSZ) so that at some distance and under (traditionally 275m... for the IBSZ in the post above, it's 220m, I think) POI is somewhere within a couple inches of the POA. That's good enough at close range to take care of the up/down part of the trajectory. After the BSZ, it's all down, and you only have to move the rear sight in one direction (up) to compensate for longer ranges.

 

[bpm990d]

The rear sight on military configuration ARs are about 1 1/3 minute for elevation.

The big aperture is offset to give you a closer zero if you are zeroed at 300m and you flip it down (hence the 0-200 marking).

If you want something more detailed, do a Google search for FM 23-9. There is a link on the ARFCOM site, but it is down.

B

 

[crak]

His was an A3 rear sight which actually does 0.75 MOA adjustments to his AR with the shortened front handle.

This pdf contains a table showing what your sights and front post do based on the configuration of your AR. Too bad I was looking at the wrong section of it until I got back home from the shoot.

 

[Lugnut]

His was an A3 rear sight which actually does 0.75 MOA adjustments to his AR with the shortened front handle.

This pdf contains a table showing what your sights and front post do based on the configuration of your AR. Too bad I was looking at the wrong section of it until I got back home from the shoot.

Thanks for all the information Chris- for some reason, even though I signed up to that forum- I can't open that pdf.

 

[crak]

I just posted it at http://www.harvardriflemen.com/AR15zero.pdf

 

[Lugnut]

I just posted it at http://www.harvardriflemen.com/AR15zero.pdf

Thanks! I can't believe Bushmaster didn't bother getting into this level of detail for the shorter gun. All the manual says is One click = 1/2 MOA... damn them.

And to boot- I'm pretty sure when I zeroed the gun, I set the elevation to the 'z' postion (instead of the 6/3 as in this pdf) so my zero was 2 clicks up from where it should have been.

Looks like I need to check the zero again and I'll be good to go.

Thanks again Chris!

 

[bpm990d]

What kind of rifle is it? Is it a 20 inch government model? The Bushmaster people have changed the names of all their stuff.

B

 

[Lugnut]

What kind of rifle is it? Is it a 20 inch government model? The Bushmaster people have changed the names of all their stuff.

B

The actual model number is XM15 ES2S, it's the M4 carbine 16" barrel with A3 sights (removable handle). It's a great gun so far... other than figuring out this sight stuff.

 

[crak]

Well, once you get it figured out it's easy to adjust precisely.

Lots of rifles are the opposite... adjustments are Minute of Hammered Drift Punch.

 

[meth0d]

Interesting stuff, I'll have to subscribe to this and refer back when I pick up the XM15 I have on lay away in Plymouth. I think it has A2 sights though...

 

[Lugnut]

I called BM today for something else and while I was on the phone with them I asked why they didn't post better instructions on zeroing in the gun. One thing I thought was kind of interesting was he said the 'z' on my A3 upper has NOTHING to do with zeroing the gun (as opposed to what the manual said directly) but was for grenade launchers... yeah.. ok. I also asked how the A3 upper could be 1/2MOA/click for all AR15 barrels (14.5" -20+")... he said it had nothing to do with barrel length. Yikes....

Thanks again for the info Chris. I hope I can make more of your training times although I still ache from the prone position.

 

[bpm990d]

That guy is a bone head.

Here is a link to FM 3-22.9. Just read chapter 4.

B