Question about zeroing an AR-16 BUIS

[DMK]

Question about zeroing an AR-15 BUIS

I have a scoped flattop with a flip up A.R.M.S. #40A rear sight. This sight has no elevation adjustment except for the height differences in the small and large arpertures.

I wish to use the Improved Battlesight Zero method, but with the large 0-200 arperture since it's the default sight when you flip it up. If I do so, what will the zero of long range arperture be?

I guess I'm trying to determine whether a same plane arperture for this sight is worth the $30. I doubt I'll even use the iron sight much, but will use them occasionally.

 

[Bartholomew Roberts]

If I do so, what will the zero of long range arperture be?

It is going to vary depending on whether the front sight base is in the rifle, midlength, or carbine position and whether it is the M4 front sight base or the M16 front sight base.

Using the small aperture with the big aperture zeroed at 50yds via the IBZ will put you between 4-6" high at 100yds, depending on the different variables. This means the far zero of the little aperture is in the 350-425yd range.

I use the ARMS #40 myself and have zeroed the small aperture at 50yds using the IBZ. The larger aperture is about 4.5 MOA low on my personal rifle; but at closer ranges it doesn't matter much (and in fact helps compensate for the height over bore of the sights in close) and at longer ranges, the smaller aperture is necessary anyway.

 

[DMK]

It is going to vary depending on whether the front sight base is in the rifle, midlength, or carbine position and whether it is the M4 front sight base or the M16 front sight base.

Good point. This is an RRA midlength carbine. I don't know what sight base it uses, but that be be compensated for by adjusting the sight post for the zero at 50Y, no?

This means the far zero of the little aperture is in the 350-425yd range.

I was sort of thinking it might be in the 300 yard area because Sanchez recommends setting the elevation to 300 when using the big arperture up close.

The larger aperture is about 4.5 MOA low on my personal rifle... in fact helps compensate for the height over bore of the sights in close...

Another very good point. The sight is about 2 1/2 inches over the bore. I think I'll go to the range tomorrow and try zeroing at 50 yards with the long range arperture, then test at 15-25 yards with the large arperture and see where it prints. It may just work out well anyway and save me the cost of a new sight.

Thnx for the help.

 

[DMK]

I use the ARMS #40 myself and have zeroed the small aperture at 50yds using the IBZ. The larger aperture is about 4.5 MOA low on my personal rifle; but at closer ranges it doesn't matter much (and in fact helps compensate for the height over bore of the sights in close) and at longer ranges, the smaller aperture is necessary anyway.

OK, I'm confused about this part. I went to the range today and sighted the small(long distance) arperture in at 50 yards. When I switched to the large(0-200) arperture, It printed about 4" lower at 50 yards and it was off the paper at 25 yards. I rezeroed the large arperture at 50 and that printed about 3" low at 25 yards.

I'm thinking that zeroing the small arperture at 50, then switching to the large arperture at close range is not helping the height of sights over bore, but making it worse.

I think I'm just going to simplify and go with the XS Sight Systems same plane arperture. With my little 16" carbine, it's doesn't have the velocity to do much good past 250 yards anyway.

 

[Bartholomew Roberts]

Yes, I've got myself backwards, it should be "high" not "low" - you would be right. The sights are still going to be 2.6" over the bore regardless of where they are printing, so if they print low, they will print even lower close up.

However, something is screwy in that if the sights are 4" low at 50, at 25yds they should only be about 3" lower than POA until you hit the near zero and then they will start to go lower again.

Also with an IBZ of 50yds, you should only be around 1.2" low at 25yds regardless of which aperture you use.

I think the same plane apeture is a worthwhile idea myself; but keep in mind that the XS version has an even larger aperture than the current large aperture you have.

 

[DMK]

However, something is screwy in that if the sights are 4" low at 50, at 25yds they should only be about 3" lower than POA until you hit the near zero and then they will start to go lower again.

Also with an IBZ of 50yds, you should only be around 1.2" low at 25yds regardless of which aperture you use.

Well, take my estimations with a grain of salt. I didn't measure, just used my uncalibrated eye. The reason it was off the paper was I'm using a double bullseye on an 8x11" piece of paper so it wouldn't have had to be too far off to miss the target completely.

I think the same plane apeture is a worthwhile idea myself; but keep in mind that the XS version has an even larger aperture than the current large aperture you have.

Yea, that big ghost sight isn't going to be too conducive to accuracy.. Still, that big ghost will be good for low light and you can switch to the little peep anytime you want so it's not too bad really.