I went to zero my ARMS 40 and my EOTech 551 today. This was on a brand new M4A1 carbine.

I wonder if I did everything correctly. I mounted the EOTech on the forward most slot on the flat top, and zeroed it without a hitch.

The ARMS was more problematic.
I mounted it on the farthest slot to the rear. And zeroed at 50 yards. I had to put alot of windage on the ARMS (much more than I expected)but eventually got it hitting center. Elevation was another matter. I bottomed out the front sight, and was still hitting several inches low at 50. I still managed to qualify with irons (I just remembered my hold over), but it was disconcerting; I like things to be a little closer. Any thoughts?

Is your front sight fixed or detachable?

Other people have posted that the fixed sight on a M4 barrel is not as high as an A2 barrel.

Fixed front sights. This isn't a kit gun-this a factory Colt M4A1 Carbine (Model R0977). The only mods thus far are the addition of a 10-year old 6V Surefire, the sling ad the sighting stuff I mentioned.

I remember from Armorer's school that there are height difference beteeen normal A2 and M4 sights, but the taller A2 sight post shouldn't make any difference, unless they accidentally put an A2 post on my weapon at the factory (and they should have caught that when they confirmed the zero at the factory). I guess I need a shorter post.

FWIW,

I've been doing alot of reading lately, and saw that Bushmaster had a problem with their production line a while back, where barrel nuts were getting over torqued.  This caused pressure to 'skew' the barrel, because the alignment pin would get bent.

The end result;  Excessive windage in the sight adjustment.

It might be something worth checking out, if all other avenues fail.  

Take a read here, at the bottom: (they talk about installing a new assembled upper, but, the idea is still pertinent)

http://www.bushmaster.com/faqs/barrels-accuracy.asp#Q: I have just installed a new upper receiver on my old barrel, and now my rifle shoots way to one side. I can adjust for the windage, but what happened here? Is my barrel no good?

Good luck,

E.

*edit - typos

First Id complain to ARMS if its a new back up sight and try to get a replacement.  If the replacement did the same thing send the upper back to Colt for a new front sight.

Mine (#38)did the same thing. It was a Model 1 M4 kit. The barrel was overtorked and caused the problems you are having. Bought a BM complete upper and had no problem. Fixed the Model one and it worked but still had a slight elevation problem.

WHat I may do is pull the ARMS 40 and put it on another carbine and see how it does; we got in 5 of these new M4s, and the first one that was issued was the one I got (big suprise, seeing as how I run our Armory). The other 4 are still sitting in the Armory and won't get issued until I can schedule a transition course for the guys they are going to, and that may be a couple of months.

Did I at least put it in the right slot on the rail?

Hey did you remember to flip it to the "up" position?

Yea I had the same problem with my old m4 upper, I replaced the front sight assembly, with a front sight assembly that had an bayonet lug. When I went to the range, my zero was off and I had to move the arms #40 11 clicks to get it zeroed..WTF!!. I sent it back to the gunsmith, and he fixed it, by putting a set screw in the bottom of the front sight, adjusted the sight/zeroed it,he tightened the set screw and then replaced the taper pins. Then I went to the range and zeroed it, 4 clicks left and all was good. but I if I was you I would reurn it and have them fixed it.

Quoted: Hey did you remember to flip it to the "up" position?

Yes.

I never even shot this rifle with the factory carry handle. Before I go sending back the sight, I'll see if I can duplicate the error on another carbine.

The Arms #40 flip up "large aperture" is a 250-300 meter battle sight that was meant for a rifle zero of 250-300 meters. Shouldn't your groups at 50 yards be high at the least and almost dead on at 25 yards?