Rear sight placement

[mlentzner]

My question is what are the 'best practices' for placement of a rear sight and part of an iron sight system?

Used iron sights plenty in the 90's US Army, but I never had a rail so I didn't get have any choice. Now that I have a modern AR-15 I can put it pretty much wherever I want.

I tried moving it forward from a fully back position, thinking it would improve my sight picture (back sight would be clearer). In practice that didn't seem to work very well. I couldn't use the smallest day sight at all (my system has four back sights of various sizes). Small targets (2" @ 50 yd) seemed to completely disappear when sighting even though I could see them quite clearly.

I am going to try moving the back sight to the same location it would be if it were part of the carry handle. I'll have to re-zero

Asking for some wisdom or experience from the group here - TIA!

[strongpoint]

I tried moving it forward from a fully back position, thinking it would improve my sight picture (back sight would be clearer). In practice that didn't seem to work very well. ... I am going to try moving the back sight to the same location it would be if it were part of the carry handle.

That would be the best approach. Remember, you don't want the rear sight clearer -- you want it to blur out. It's also harder to see through a small aperture from farther away, obviously. Mount the rear sight as far back as is feasible, unless it's designed to be mounted otherwise.

[as_rocketman]

It appears we're talking about aperture iron sights, and if so, you want it as close to the eye as practical.

The purpose of the aperture is to put your eye in alignment. If your eye was in the right spot, you wouldn't need the aperture at all -- just look at the front post. The only reason we need an aperture is that we can't guarantee where the eye goes otherwise.

Since that's the function of the aperture, the farther away it is from the eye, the less precise it will be as a guide. Moving it nearer to the eye narrows the light cone from the front sight through the aperture -- and it also makes the aperture appear larger, which in turn allows you to see the target better.

There have been quantitative studies on how much point-of-impact is affected by not having the front post precisely centered in the aperture, and it is much less of a problem than you might suspect. So don't strain trying to make sure the alignment is perfect, instead just let it happen naturally.

If we're not talking about aperture sights, the above is no longer true. Open or buckhorn sights must not be too close to the eye because you now have to resolve the rear sight to get proper alignment. In this case putting the rear sight about 1/3 along the barrel is recommended -- which is just the way it's usually done. But this also explains why aperture sights are more accurate, all else being equal.

[Jesse Tischauser]

I've always gone with the longest sight radius possible being the most accurate. Competition shooters will actually cut an extra notch in their picatinny rail to get an extra 1/8" rearward.

[mlentzner]

Thanks for all the info guys.

@as_rocketman - that's a great explanation of the difference between an aperture and open sight. And yes I'm using an adjustable CZ sight that is very similar to a standard military M16 sight.