AR-15 Front Sight

[flygrimm]

I have had a Bushmaster XM15E2S since the early 1990's. Pre ban. When I got the rifle the front sight was canted to the left far enough to where it was clearly visible. Back to Bushmaster and they fixed it. I hardly shoot the thing. On reason is that even though the front sight looks OK now I still need 15 clicks left windage to center the shot group at 50 yards. Question is how far out of alignment does it have to be to make that kind of windage adjustment? Like I said it looks pretty straight but I can't really tell. I did center the rear sight and ran a string through the aperture to the front sight post and it looks like it is centered over the barrel and the gas tube also appears to be centered over the barrel as well.

The only thing I have noticed is that the left protector ear is thicker than the one on the right. Maybe the front sight base is poorly machined?

I have been toying with the idea of removing the sight base and drilling out the holes for set screws thereby making it adjustable.

What do you think?

[aubie515]

So you are just sighting in a rifle you owned since the 90s now? The tab thickness should not have anything to do with you sighting in unless the thicker tab is pushing on your sight post.

I would recommend taking a picture from behind the rifle, so we can see the front and rear sights. Also picture from front to back as well.

Older Bushmasters should be GTG as I owned one from the 90s and I never had any issues with the irons.

[flygrimm]

I don't shoot it much. I pull it out of the safe, shoot it a bit, get frustrated with it and chuck it back in the safe. It's been to Bushmaster twice and they say there is nothing wrong with it. I don't have this issue with any of my other rifles but maybe there is something wrong with my technique. Just left for work today so won't be able to get any pics till Thursday or so.

[eyecanshoot]

Question is how far out of alignment does it have to be to make that kind of windage adjustment?

About 15 clicks out of alignment. I couldn't resist.

I have this same issue with both of my AR Rifles. I don't actually think it is the front sight post causing the issue. I think it is caused by the straight stock not letting me get lined up properly. When using irons I really need to mash my cheek bone into the stock and it is very uncomfortable.

If I install my scope at 1/3 cowitness the vertical crosshair lines up perfectly with the front sight post. This tells me that the front post should be correctly oriented. The extra height that 1/3 cowitness provides seems to be the minimum clearance I need to get lined up properly.

The iron sights are not tall enough to be using with a straight stock. I think this causes problems for a lot of people and probably why red dots are so popular.

[jamf]

Bore sight it at a plumb vertical line like the edge of a building or something and see if its lined up.
That's what I do before I pin a sight tower.

Its possible that you are not getting a proper sight picture.
Try someone else's AR if that's your only one and see if you shoot to point of aim with it.

[aubie515]

I"m in Pottstown, if you want to meet up to see what we can do to resolve your issue with your sight.

[flygrimm]

aubie

Thanks for the offer. I'll contact you when I get home from this trip.

Stuart

[flygrimm]

An update.

Disassembled the rifle, trued up the face of the upper receiver cleaned all mating surfaces and reassembled. No changes. Still requires 15 to 20 clicks left to get centered on target. Called Bushmaster just for some advice. Tech suggested replacing the upper receiver as the carry handle may be machined out of wack. Kind of an expensive thing to try. Maybe save that for later.

Also tried shooting left handed. That was a trip. No change that way either.

Took a couple of pictures as recommended above. Also tried the bore sight thing. That seems right on with the rear sight centered and the bore aimed at a vertical line about 100 feet away.

rsz_dscn2463.jpgrsz_dscn2464.jpg

I think my next course of action is to make the front sight/gas block adjustable. But anyone have an idea how much I might have to rotate the front sight to center the rear? If it's going to be too much it will look weird and may end up blocking the gas port and disabling the rifle.

Or maybe just operator error. Anybody shoot at the Keystone Rod and Gun Club in Bath, PA? If so we can meet up and I'll let you have a go at it.

Stuart

[Bang]

The front sight, according to your photo, appears quite centered. You are unhappy that the rear aperture requires 15 to 20 clicks left of physical center to be zeroed windage-wise. I would think that in order to center the rear sight, the front sight would need to be moved right the equivalent of 15-20 clicks...in which case a compromise 8 clicks right on the front sight and 8 clicks left on the rear sight would be the best you could do, if cosmetic appearance is important.

It might make you feel better to learn that many .30 caliber M1 Carbines require the rear aperture to be adjusted considerably left. Once adjusted, the rifles perform normally throughout their near, mid and far ranges, as would your Bushmaster.

[flygrimm]

I figure it's probably more a cosmetic thing, it just bugs the crap out of me.

Stuart