M4 type AR sighting

[Freakhouse]

Ok, so here is the issue. I have an M4 style AR-15 that was built from a fairly reputable kit. It is a flattop with a Mil-Spec carrying handle and rear sight. It functions flawlessly.

However, with the rear sight set to 6/3 and the front sight pin set as high as I am comfortably willing to go, and beyond (about .050 of space between the forward sight base and the locking ring, and the top of the sight well above the side wings) the rifle is still shooting about 12 inches high at 100 yards.

Other than going with an extended front sight pin, or a reduced height rear sight, is there anything else that I could possibly do to fix the situation besides sending it back in for work? I don't believe that I have the F type front sight base, but even at that I don't think it would be enough to account for what I am seeing.

Any suggestions or hints would be much appreciated.

Thanks in advance!

Brenton

 

[MisterPX]

How's your sight picture?
Can you zero at 25M?

 

[pgeleven]

yeah id zero that thing at a closer range, and if youre committed to having a carrying handle type rear sight, try purchasing a 'flip up' type. its fixable bu youll have to do some homework and maybe settle for a red-dot or glass

 

[Onmilo]

Look at the left side of the front sight housing.
If it is the correct one for a mil-spec flattop it will have a forge mark that goes something like 'F06EB'

If your sight housing does not have the 'F' in the forging mark it is a standard sight tower and you will need the taller front sight post to correctly regulate the sight.
I have yet to see a cast front sight tower that is the correct height for a flattop.
You could also use a tritium front sight post as all of these I have used are more than generous in the sight regulating height and ability.

You may have the correct F marked front sight housing and a taller non mil-spec flattop too.

Either way the best and least expensive beginning attempt is to use a taller front sight post.
You can buy these from Bushmaster and others, I like Bushmaster because they don't way overprice these taller sight posts.

 

[Bartholomew Roberts]

Yes, it is at least partially a front sight base issue. You need a taller front sight post. You may also be the lucky recipient of a receiver or front sight base that is "a few .001"s off; but not something anyone would notice." These are sometimes resold to the "budget" parts warehouses after they are rejected by other dealers.

 

[slugcatcher]

You have a standard ar-15 front sight assy on an m-4 style rifle. This is common with the kit companys out there. Bushmaster sells a taller front sight post for around $5. That is the cheapest way to fix the problem.

 

[frenchbushmaster]

+1 with slugcatcher

Exactly the same problem for one of my friend here.
It's the good solution not expensive and easy.

 

[Jeremy2171]

Or he could simply adjust his rear sight which sounds like its not calibrated. For M4 style rifles the rear sight needs to be at 6/3-6 (thats down six clicks) for the 100yd zero.

If you have an A2 rear sight it should go down to "8/3" then minus 3 more clicks.

If it's an A4 then it will be "6/3" -6 clicks.

If your rear sight bottoms out at 8/3 (6/3) and moves no more then your rear sight is improperly calibrated.

The Army uses this method but the Marine Corps adjusts them so they will go down to the -3 or -6.

To calibrate it:
Set sight to 8/3 (or 6/3) then flip the small aperature up so you can look down at the top of the sight and you will a small set screw. Get a 1/16" hex key and loosen the setscrew a few turns.

Then take the elevation drum and turn the BOTTOM (it has an upper and lower part) to the rear about 1/8 turn then snug up the setcrew. See how many clicks down you now have. Adjust the drum again if you need too.