Project Appleseed

How to properly set up your sights, from USMC M16A2 manual.

Good info but beware... A4 and mid length stocks have shorter site radius and barrels. This will effect trajectory and velocities. Now would be the time to post the right answers but I am .pdf inept. I have the A4 info but the jury was still out on MOA adjustments for mid length forends. I guess the best policy might be to limit engagements with 5.56 to within 150-200m where the velocities are still up there and the majic of sewing machine needles flying at lightspeed works. Or, choose USGI .30 cal equipment for those tangos up close and way out there.
Weighing in, Sheepdog

Why is there a need to take the rear elevation knob one click up during zeroing, and one click back when the zero is complete? I have never understood this...

Quote from: Tackleberry on December 25, 2008, 01:51:19 PM
Why is there a need to take the rear elevation knob one click up during zeroing, and one click back when the zero is complete? I have never understood this...

It has something to do with the trajectory of the 5.56 round so that when you zero at 25M, with only a click or two of adjustment (during the zero process), you'll never have to adjust it at all in the field and will still be able to make "center mass hits" all the way out to 400M. Without that exta click or two it will drop another few MOA out to 400 and would cause a miss.

Basically, it's a lot easier to have everyone do a click or two during zero to set up their rifles so they don't have to remember "how many clicks do I need for 353 yds?" out in the field because they'll forget. Everything on the M-16A2 is set up to take the guess work (or all thinking for that matter) away from the individual soldier and provide them with a rifle that will hit out to 400M with NO thinking required.

There's a little more thinking after that, but not much because the rear sight has numbers on it. 500M shot? OK, click up to 5. 700M... you got it! Click up to 7! 


As Sheepdog pointed out, this applies for the A2 with 20in. barrel. The various other models are going to be slightly different at range. They too, however, are set up to get the maximum amount of hits at range and take the guesswork away from the shooter.

I think the one click up has to do with the elevation wheel design- it's got spring loaded ball bearings pressed into holes which index the wheel, that's what makes the clicking sound.  What if the wheel is rotated such that it presents the ball bearing not with a hole but with the edge between two holes?  What if this condition happens when the wheel is fully twisted to the rear sight's lowest position?  Plus, to properly index that wheel into its starting position, the flat 8/3 side of the wheel has to point due west (if the barrel axis points north, stock points south).
When the wheel is completely bottomed out, the wheel flat is slightly pointing southwest, the ball isn't in the hole, for one, but more importantly the wheel isn't lined up properly with the 8/3 flat pointing due west. 
So the sight design requires you to start having achieved:
  a fully indexed click,
  a due west 8/3 face with rear sight at low elevation. 
and are now ready to adjust that front post. 

Isn't that extra partial click of wheel travel a nuisance, though?  Why wouldn't the designer size parts such that the sight avoids this partial click altogether, and we start out with the wheel pointing due west every time?
Might have been done to allow for accumulation of sand.  Get a little sand in there, and you'd never be able to lower the sight to the 8/3 position without first giving the parts some clearance. You've got two large, flat surfaces between sight ears and receiver top; grit there is more likely to impede the intended range of motion of the rear sight assembly the lesser the clearance given.     

Thank you, FM. 

Its always good to re-read zeroing technique, it makes
a good handout also.

Thanks for the input guys...

It's 1 click up when zeroing, because the trajectory calls for it. It's one click back after zeroing, so you're on for 300. If you zero at 300 (no clicks), you are going to be eroed too high.

I've seen firsthand the effects of zeroing at 300 or 300 -1 click, on a military qualification range. The qualification scores absolutely sucked. Next time around, they zeroed at 300 +1 click, and the scores all improved.

Roger the above - the same principle applies to zeroing the M4 with the Backup Iron Sights (BUIS) - you set the BUIS on a white line between 200 and 300m to zero at 25, and that is your 300m battlesight zero.  Note that Line of Sight for the M16 and M4 BOTH is +2.5 inches over the bore, although of course the 14.5" barrel will have a different trajectory due to differing sight radius as well as muzzle velocity.

A Google Search shows the following data for the M193 and M855 rounds fired out of the M16A2 -

              5.56 NATO Ball Ammunition Ballistic Comparison
                   based on Aberdeen Proving Ground Data
           velocity (fps)    trajectory (in.)    drop (inches)    drift (inches)*
range   M193   M855       M193  M855      M193   M855   M193    M855
(meters)
  0       3,200  3,100     -2.5      -2.5       0.0       0.0      0.0       0.0
100      2,774  2,751     +2.8     +4.4      -2.2     -2.3      1.3       1.1
200      2,374  2,420     +2.7     +5.8      -9.9    -10.2      5.8       4.9
300      2,012  2,115     -4.9       0.0     -25.1    -25.3     14.2    11.8
400      1,680  1,833    -23.0    -15.0     -50.8    -49.5     27.6    22.4
500      1,373  1,569    -56.2    -42.9     -91.6    -86.7     47.5    38.0
600      1,106  1,323   -113.1   -88.2    -156.1  -141.3     76.4    59.5
700        995  1,106    -206.8  -156.1    -257.3 -220.9    113.5    88.4
800        927  1,010    -339.9  -267.7    -398.0 -339.2    156.1   124.9
                                                                  * Drift for 10 mph wind.
M193 Ball ammunition fired in M16A1 rifle with 250 meter battle sight zero.
M855 Ball ammunition fired in M16A2 rifle with 300 meter battle sight zero.

Interestingly, and notwithstanding the above, we zero the M68 Close Combat Optic to point of aim/point of impact at 25. 

I do not have the ballistics data for the M4, but I note that the listed velocity for it is 2,970 FPS, 130 less that its 20" barrelled cousin.  I also note that the M4 is mechanically zeroed at the 6/3 rear sight elevation setting when using the standard sight on the removable carry handle.  Most of all, I note that the new manual states 'NOTE: Mechanically zeroing the weapon is only necessary when the weapon zero is questionable, the weapon is newly assigned to the unit, or the weapon sights have been serviced.'

As an aside, an excellent comparison of trajectories of the M855 in the M4 and M16 rifles is in FM 3-22.9 JUN 08. which is readily available on the 'Net.

Hold 'em and Squeeze 'em!

I searched and searched and searched for the ballistics info, specifically the drop and drift for the M-16A2 one night for several hours. I ended up with the table above (from Aberdeen) and then came to the conclusion that it was so hard to find because it's never been necessary.

There really is no need to know the drop (and subsequent comeups required) because it's already been figured out for you. Matter of fact, they don't want you to know! If you're trying to do math in your head, it's going to take you way too long and by that time, the bad guy is already going to shoot you. (Because he knows his bullet's drop and subsequent comeups required to shoot you at range.) 

If you lucked out and you're in a unit with a super high-speed First Sergeant or someone else coming out to visit you while you're holding your rifle, maybe they'll quiz you "Troop, close your eyes and click your rifle up to 700 meters. DO IT NOW!" But I doubt even that guy will know the bullet drop of the M855 at that range.

Well, if you really must know, it's out there. But, with the M-16A2, there's absolutely no guesswork. Provided you remembered to sight it in with your +1 click!


Oh, and since this is the Appleseed website - DON'T have your AS attendees sight in early on Saturday morning using their 1" sighter squares and then click down to their "BSZ" for use during the rest of the day. (Cause someone will try!) Also, make sure they're using the SMALL peep and not their 0-2 big ol' holes. I don't know how many people have told me "well, we're only shooting at 25 so I thought I should use the 0-2 cause that's good for all the way out to 200 yards, right?" You'll see a lot of smiles after you walk down to the target line once you've flipped that peep down. "Wow, it's like, half the size of what I was shooting before. Cool!" (Which will be immediately followed by) "Now, don't I need to like, click it a few clicks because I'm using the 300 yard sight?"