M16A2 Long Range with Iron Sights Dilema

[JoeSmith]

I was shooting M16A2 1/7 twist barrel with M885 green tip and standard iron sights, zeroed on standard A2 25m target; shot the usual out to 300m with 3/8 on the rear sight and transitioned to steel at 400m, dialed 4 on the rear. Missed. Had a spotter bring up the sights till I was at 5. Hmm.
Went to the 500m steel. Had to dial 6. ??. Went to 625m. Had to dial 7+1 click to hit it.
Shot the 700m steel and dialed 8+3 to hit it.
My question is-what is going on? If the target is at 400 or whatever, shouldn't the rear sight elevation correspond? Why is it so off?
Thanks.

 

[Graham]

Re: M16A2 Long Range with Iron Sights Dilema

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Shooter5</div><div class="ubbcode-body">Why is it so off?</div></div>
1. <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Shooter5</div><div class="ubbcode-body">I was shooting... M885 green tip...</div></div>
2. The markings on the sight do not correspond to 100 meter increments of range. All loads do not take identical dope. ENV and MET conditions change.

 

[JoeSmith]

Re: M16A2 Long Range with Iron Sights Dilema

All very well and good, 855 requirement is like, what, 4moa? However, thats a MPI average, not that large vertical drop. But I have shot old M193 and I don't remember it being that far off.

 

[Graham]

Re: M16A2 Long Range with Iron Sights Dilema

Service rifle rear sight adjustments are 1 MOA elevation and half-MOA wind.

Now you know that guesses equal misses.

You've got to know your come-ups in MOA's. Right now, you don't even know whether your sights are mechanically accurate.

Post your actual dope, in MOA's, for the ranges you were shooting at. Compare that with the dope, in MOA's, that you were dialing.

What was the windage you were dialing at each range to get hits with that ammo?

 

[JoeSmith]

Re: M16A2 Long Range with Iron Sights Dilema

Windage-too easy. Center hold for most shots, left favors for others.
MOA for the elevation-the rear sight on the A2 only has the course 4 or so clicks in between each number. Not much options there.