I have a 20" FN flattop upper.  I have an unknown carry handle that has the 3/6 adjustment knob for elevation.  My question is when I attempt to zero the rifle at 25 meters my front sight post was maxed to the down position and I was still shooting low.  Out of desperation I adjusted the elevation wheel to 600 meters and I was finally hitting point of aim at 25 meters.  Could I have a "bad" carry handle/rear sight?

Carry handles are made in various heights.
For example Bushmaster made odd height carry handles.

The "made in China" $29.95 carry handles are junk. Without knowing who made yours I can't tell you if it's the problem or not.

Your front sight tower should be marked with an "F", which designates it was designed to be used with a flat top receiver.

I have been using Rock River Arms national match carry handles because they work and have 1/4x1/4 clicks instead of the courser 1/2x1/2 which is the G.I. standard.

Your front sight post can be screwed down (clockwise) to reduce the need for having the rear sight setting so high.

With the very high sight over bore distance on an AR, you'll need a lot of rear elevation to zero at that short of a distance and the subsequent trajectory will put you very high at 50 and 100 yards/meters plus a lot of distance sensitivity even at other short ranges .

I know it's not the question you asked,  but you might want to run one of the online ballistic programs and see what the trajectory ends up being for yourself (take a look at the point of impact for even just 20 or 30 yards leg along 15 or 35 yards - you'll find yourself off just at 50 yards by a substantial amount that will have to be compensated for in your poa).  In my opinion, your adjustment is fine and probably expected but the usefulness of that zero at even modestly different distances is hard to use. You might be better off going for a more standard 50 yard zero and knowing the holdover for 25 yards/meters.

Zeroing for very short distances cause a lot of holdover of other, not that different distances, which can really make things hard to use.

My iron-sights rifle is zeroed to 25, but I'd advise that you go with a 50 once you get a good zero at 25. 25 is also a 300 zero, which is nice if you shoot irons at 300. I believe that 50 is also zeroed at 200, which is more practical, and it's a generally "flatter" zero with a lot less distance sensitivity.

Okay, so my carry handle is probably not matched to my front sight.  The front sight is an "F" marked and my carry handle looks to be a commercial spec.  My goal was to get a good zero at 25m for Appleseed events.  I did qual when I used my 10/22 I just wanted to try with an iron sighted 20 inch AR.  I would rather not have to use any hold over.  Thanks for the insight on different zeros.

I was going to suggest filing down your front sight, as sully mentioned.

The rear elevation wheel can also be adjusted (as in the RIBZ).  For the RIBZ you would raise it to allow to actually go lower, so I doubt that is the problem (was originally thinking it may not have been set correctly on yours)

The cheapest route would be to take the front site post and "shave" off some.  This would allow me to keep my carry handle.  Without measuring at looks like I would have to remove about .06".  Hmm, besides a shorter front site post would I have any other issues?

If you are using a 50 yd zero, then you should be shooting about 2-1/2" low at 10 yds (30 feet).  Here is a video showing this by Frank Proctor:

https://www.youtube.com/watch?v=P-FUsH8jt6E

Installed a new set of AeroPresision front and rear flip sight on my BCM headed out to the range to zero in at 50 yds. Windage was no problem, the problem is elevation. POI is about six inches low, and the front sight post is bottomed out (too big of a sight post?). Anyone here have the same problem using Aero?

Something is fubard.

A flat top rifle length system should be zeroed with the rear drum at 6/3 + 2 clicks for a 25 meter zero as a starting point.

If you are bottomed out at the front sight, and need to add an additional 10 + minutes to the rear sight to zero at 25 then i would say something is not quite right with that upper or your perhaps your carry handle.

Thanks, I'll give it a try.

"F" Marked Front Sight Base


There is no difference in the overall height of an “F” marked front sight base and a standard front sight base. The only difference between the two front sight bases is the height of the sight “shelf” above the top of the barrel.



The front sight post on a standard Colt front sight base will bottom-out in the sight well at approximately 24 clicks below flush. On an “F” marked front sight base the sight “shelf” is a whopping 0.040” higher than on a standard front sight base. That means you might have to turn your front sight post down approximately 6 clicks further with an “F” marked front sight base than on a standard front sight base. (6 whole clicks difference. Oh, the inhumanity!) So unless your front sight post is set at 18 clicks below flush with a standard front sight base, using an “F” marked front sight base on a 20" barrel will be a non-issue.


The fact of the matter remains: if you have a standard FSB and a 16” barrel, you may need a Bushmaster sight post to make up for the .040” that you have lost on the height to the neck. It is irrelevant for the 20” MSR’s, as you will not have any issues when zeroing the rifle. The “F” mark was introduced for the Marine Corps, so that armorers had a 1-piece replacement for all carbines and rifles. Since the military is where the design comes from, a lot of manufacturers follow suit. Lack of consumer education and the “Mil- Spec movement”, for lack of better terms, have made this overly complicated, when it is really very simple.
When you have a full-length rifle barrel, you don't need a higher front sight, and if you've got a carbine, you do. Whether the extra .040 inch comes from a higher base, or a higher blade, is totally irrelevant.
Bushmaster has only one height sight post. Our commercial made rifles utilize the proper height front sight post that can be used on any standard FSB to give the adjustments needed.
So to sum it up: if you have a standard front sight base and have trouble zeroing it, then you need a Bushmaster front sight post. Again, we only have one height, which is what the consumer needs. Please refer to the above picture for reference.