View Full Version : Elevation Drum Binding
I have a detachable carry handle sight with the two-part elevation drum held together by an allen screw. The bottom part of the drum actually raises and lowers the rear sight apertures, while the top of the drum bears the elevation markings. With the allen screw removed, the top portion of the drum is supposed to rotate freely. On my carry handle sight, the top part of the drum will only rotate freely when I have raised the sight almost all the way up; it binds in the lower positions. This makes it difficult to set calibrations, for example to back off a certain number of clicks from the very bottom position and then move the "6/3" back into alignment by rotating the upper part of the drum. What's up with that?
First question: Do you have M16A2 rear sight parts in your detachable handle? There are differences in the elevation drum, index and rear sight base.
Have you inspected everything for burrs?
For those that may not know: The way the sight was designed to work was the elevation drum is set at 6/3, loosen the setscrew so that it locks the elevation index in place and zero the rifle at 300 meters. Then screw the setscrew back into place.
https://i.imgur.com/q2GkLvg.png
First question: Do you have M16A2 rear sight parts in your detachable handle? There are differences in the elevation drum, index and rear sight base.
Have you inspected everything for burrs?
For those that may not know: The way the sight was designed to work was the elevation drum is set at 6/3, loosen the setscrew so that it locks the elevation index in place and zero the rifle at 300 meters. Then screw the setscrew back into place.
I actually have two carry handle sights with this same problem: a PSA mil-spec and a UTG PRO mil-spec; the description of the UTG specifically states that it has an A2 sight assembly and will fit the M4.
I actually have two carry handle sights with this same problem: a PSA mil-spec and a UTG PRO mil-spec; the description of the UTG specifically states that it has an A2 sight assembly and will fit the M4.
It's curious that PSA and UTG would call it mil spec. I'd seriously consider finding a Colt take off if you want to use the field sight.
I actually have two carry handle sights with this same problem: a PSA mil-spec and a UTG PRO mil-spec; the description of the UTG specifically states that it has an A2 sight assembly and will fit the M4.
It's curious that PSA and UTG would call it mil spec. I'd seriously consider finding a Colt take off if you want to use the field sight.
I actually have two carry handle sights with this same problem: a PSA mil-spec and a UTG PRO mil-spec; the description of the UTG specifically states that it has an A2 sight assembly and will fit the M4.
Shows what they know . . .
Did they think to consider that the M4 carry handle rear sight takes one revolution of the elevation knob to go from a 300 meter zero to a 600 meter zero, but an M16A2 goes from 300 to 800 meters in that same one revolution?
You may want to drive out the bottom spring pin and check all the parts for burrs and damage.
There's a Colt A2 carry handle assembly in the Equipment Exchange right now that's priced at $120 shipped.
I bought two of them a few years ago for about $100 each, so considering the current market, this is priced fairly.
Or keep using bottom tier components, with the problems they cause.
Here we go again, with the duplicate posts.......
There's a Colt A2 carry handle assembly in the Equipment Exchange right now that's priced at $120 shipped.
I bought two of them a few years ago for about $100 each, so considering the current market, this is priced fairly.
Or keep using bottom tier components, with the problems they cause.
If you are vigilant you might find one at a gunshow for $50-75.
To the OP:
The probable cause of your binding is rough finish on the parts, With the knob all the way down the spring is full compressed, when all the way up the spring is at its longest length.
There's a Colt A2 carry handle assembly in the Equipment Exchange right now that's priced at $120 shipped.
I bought two of them a few years ago for about $100 each, so considering the current market, this is priced fairly.
Or keep using bottom tier components, with the problems they cause.
If you are vigilant you might find one at a gunshow for $50-75.
To the OP:
The probable cause of your binding is rough finish on the parts, With the knob all the way down the spring is full compressed, when all the way up the spring is at its longest length.
Did they think to consider that the M4 carry handle rear sight takes one revolution of the elevation knob to go from a 300 meter zero to a 600 meter zero, but an M16A2 goes from 300 to 800 meters in that same one revolution?
So is this guy mistaken?
https://www.youtube.com/watch?v=wzINqoSP4Eo
So is this guy mistaken?
https://www.youtube.com/watch?v=wzINqoSP4Eo
1) If you are going to zero any of the M16A2 style rear sights per the Army FM, you do not mess with the elevation setscrew, period. You just leave the rear sight the way it came from the factory, which should have 8/3 or 6/3, 3-clicks up from all the way down and if it isn't, it doesn't matter. In fact, the Army's FM 3-22.9 - Rifle Marksmanship M16/M4 Series Weapons, never even mentions the fact that the elevation knob and elevation index are separate and the setscrew even exists. Even the USMC manual notes that messing with the setscrew is an armorer's function. So, as far as the military's concerned, the elevation knob and index are a solid mass that never moves.
2) If zero an M16A2 per the FM (with a 25 meter reduced size zero target), you get a pseudo-300 meter zero, based on a lot of assumptions about the trajectory and the sight. How the Army wrote the manual and how the sight was intended to work are two different things, even though they both get you to the same place. The USMC manual has zeroing taking place at a 300 meter KDR, or at 36 yards as an expedient.
3) I didn't hear the guy reference the M16A2 versus the carry handle rear sight so I can't say.
I didn't hear the guy reference the M16A2 versus the carry handle rear sight.
The guy shows a carry handle sight with the 6/3 drum and refers to it as an "A2 rear sight."
The guy shows a carry handle sight with the 6/3 drum and refers to it as an "A2 rear sight."
An M16A2 rear sight elevation index makes one revolution and goes from 300 to 800 meters in 25 clicks.
The carry handle rear sight elevation index makes one revolution and goes from 300 to 600 meters in 24 clicks.
https://i.imgur.com/q2GkLvg.png
Upon rereading this thread, I noticed that this illustration provides a possible explanation for another problem with my carry handle sights. I've got three identical sights, but they vary in the number of total clicks available. From the bottom position I make one full revolution of the drum and then count the extra clicks I have available before I top out. Sight number one gives me three extra clicks; sight number two, five; and sight number three, eight. If I wanted to set up a RIBZ--which requires six extra clicks below the 300 meter setting--sight number three would be the only one I could do it with and still be able to go all the way up to the 600 meter setting.
The illustration shows a vertically-oriented slot cut through the lower portion of the threaded part of the rear sight base, a roll pin inserted through the slot to keep the enclosed spring in place. It would appear, then, that the total number of clicks would depend on the length of the slot, slight variations in the milling of the slots possibly accounting for the variations in the total number of clicks.
Thoughts?
That makes sense to me. Seems the main cross pin captures the sight base, the spring keeps tension, and the slot you mention is what allows vertical movement, while allowing no appreciable rotational movement (just that little wiggle present on A2/A3 sight bases).
You have located the discrepancies, it would seem 👍
That makes sense to me. Seems the main cross pin captures the sight base, the spring keeps tension, and the slot you mention is what allows vertical movement, while allowing no appreciable rotational movement (just that little wiggle present on A2/A3 sight bases).
You have located the discrepancies, it would seem 👍
I'm now mulling over possible remedies. What about having the slot milled all the way out through the bottom and then welding or epoxying a small, thin washer across the bottom that would butt up against the roll pin when the adjustment tops out?
I wouldn't cut it all the way. A little adjustment would probably go a good ways. A small round needle file would do it.
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