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TheSadPanda 09-01-2011 07:53 PM

Having trouble with the iron sights
I recently purchased a new SIG M400 AR and put on a magpul BUIS, but kept the front post on. So naturally I want to sight the irons in before I get a red dot, but I just simply can't do it. In order to sight in you have to get a grouping to move around. I cant get anything even close to a group. heck, @ 50yds I'm not even on the paper half of the time. I'd swear I'm in the correct sight position, and I'm not anticipating recoil. So does anybody know what I could possibly be doing wrong, and how I could fix it? :o

Snakedriver 09-01-2011 08:21 PM

If your SIG AR is shooting all over the place like that at 50 yards, something is way loose. No way it should be like that. Check to make sure that everything is tightened properly, but don't over torque anything. Is the MBUS throughbolt centered and seated in the rearmost notch/slot on your flat top? Also, what ammo are you shooting? The wrong ammo can cause wild shots depending on your barrel.

Try moving closer to the target, to say at 25 yards to get a better idea of where you are shooting. The front sight is adjustable for elevation (vertical), the rear MBUS sight will only be adjustable for windage (horizontal). Adjust one direction at a time starting with the vertical. Once you get the vertical point of impact to agree with your point of aim, adjust the horizontal impact to bring it into agreement with your point of aim. That should give you a pretty good zero.

A picture of your set-up may be helpful too.

Sniper03 09-01-2011 08:22 PM


If you can be a little more precise about what is happening on the target. Example hitting high most of the time, low most of the time, or shot group is Just all over the place left and right, high and low.
It is a 1:7 twist rifle so it should not be the effect of barrel twist. Just let us know! What ammunition are you shooting Brand and Grain, reload or factory. Could be a problem with assembly. Like a loose barrel nut or a bad barrel. It happens!


TheSadPanda 09-01-2011 08:29 PM

2 Attachment(s)
I'm just uploading these pics right before work. I understand how the basic sighting in process goes, but I just can't seem to get any consistency. could it have anything to do with lubing or lack there of? I'm shooting american eagle .223 55 gr. The shots are just everywhere. I have literally no set direction im off by. It could very easily be me as well as the gun I think.

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Attachment 32469

Sniper03 09-01-2011 09:05 PM

Do you have any other rifles with iron sights. Just for kicks you might shoot it to see if you are having the same problems. If you are it is something that you are doing. If you shoot it well then we need to start looking at the weapon. The American Eagle FMJs are good training and practice ammunition. In fact on the SWAT Team we used them for training and the shot equally as well as our standard operations ammunition which is rare when you switch to training rounds due to cost. The other thing you might do is if you are going to get an optic go ahead and get it and install it. Get it sighted in. If you have no problems then we are back to something going on with the iron sights or maybe how you are looking through them. I know the BUIS is designed to have a large rear aperture since they were designed for CQB. In my case my eyes are not what they use to be. So sometimes I have difficulty seeing the irons that well anymore. And the fact that the BUIS has a large hole (Aperture) in the rear sight this might add to the problem. The only thing that throws me is the 50 yard distance? And missing the target completely. How big is the target you are using. Just some ideas! We will be here to help. Shoot it off of a rest to check for accuracy.


Jpyle 09-01-2011 09:47 PM

Are you shooting off-hand or from a rest? Do you have the rear sight set to the proper aperture? Is the front sight indexed properly, sight post tight (not wobbly in base).

Have you tried use a bore sight laser to align the sights before trying to zero?

TheSadPanda 09-01-2011 09:47 PM

I wont be able to afford a red dot until the end of the year, so im kind of stuck with the iron sights :( the BUIS has the dual apertures (small and big) and ive tried both with almost the exact same results. The tagets are the standard 10 or 12" circles. Ironically, my only other rifle with iron sights was so bad from the factory that i can visually see how crooked the back sight is. I shoot handguns just fine with regular sights.

Ps- im sorry for any spelling errors, im writing this on my phone.

FCross7 09-01-2011 09:57 PM

I would let someone else, maybe someone who works at the range, shoot the rifle and see if they get the same results. That way you can at least narrow it down to either you or the rifle. If it does turn out to be the rifle, I'd give SIG a call and see what they have to say.


Quentin 09-01-2011 10:11 PM

Panda, have you tried shooting from a sandbag or other rest like JPyle mentioned? If you haven't yet try it starting out at 25 yards. You should be on the paper and be able to group. Oh, how's your eyesight, if the sights are blurry it's hard to get a good group shooting offhand.

TheSadPanda 09-01-2011 11:03 PM

Im not sure who else i could get to fire the rifle that knows what theyre doing. But ill see what i can do, because its definitely worth knowing if its me or the rifle. I did all this shooting from a bench with the front rested on a black with my hand in between. My eyesight is almost perfect. Im forced to shoot rifles with my non-dominant eye, but its never been a problem for me before.

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