I've got an ARMS 40 BUIS on my Bushmaster M4 and was curious as what the proper battle zero is for this particular sight. I got it sighted in on a 25 Meter M16 target, with the small apeture. When I switch to the large apeture it shoots about 4" low. I'm getting good groups, just wanting to know what the proper method is. Also what kind of bullet drop am I looking at, say dead on at 25M, what would my 100, 200, and 300M bullet trajectory be, using 55gr ball ammo. A couple inches hight at 100, dead on at 200 and a couple inches low at 300M? If anyone knows from experience please share, ranges and open fields are not too common up here in Wisconsin.

thanks Billy

Sight it in at 50 meters/yards for best results. Use the small aperature to sight it in, then flip to the larger one if you prefer once it is. This will keep the bullet closest to your point of aim out to 300 meters/yards or so if I remember correctly. It's much better than 25 yards for distance shooting.

25m zero is out for the AR15.  And for most all rifles for that matter.  Zero the AR at 50yards or Zero it to be 2 inches high at 100yards/meters would be better (same trajectory as 50 yard zero).  At 150 about 2.5 inches high, then at 200 youll be dead on.  250 will be 2 inches low.  At  300 it will be something like 4 or 6 inches low, but thats only 2 MOA and not even worth compensating for with most people an iron sights since most people are only capable of about 2 MOA iron sighted anyway.

Quoted: Sight it in at 50 meters/yards for best results. Use the small aperature to sight it in, then flip to the larger one if you prefer once it is. .

Are these two apps on the same plane? If you intend to use the large as a back up, wouldn't it be better to sight it with the large?

Quoted: Quoted: Sight it in at 50 meters/yards for best results. Use the small aperature to sight it in, then flip to the larger one if you prefer once it is. . Are these two apps on the same plane? If you intend to use the large as a back up, wouldn't it be better to sight it with the large?

Yes, they are in the same 'plane'. Its more precise to zero with the small aperature because you have less margin for error in centering the front sight post within the rear aperature.

as i recall the large app is slightly right of the small one.  when you move to one or the other i think it shifts left and right a small ammount.   but it's not critical.  the large one is for 25 yds and closer.  the small is for 100 yds and further..  between you can use either.

Quoted: Are these two apps on the same plane?

No they are NOT on the same plane.  The large aperture is anywhere from 2-6moa below the small aperture (depending on sight radius and who manufactured the sight).

Zero at 50y with the sight you intend to use - remember it's a 'BACKUP' iron sight.  I generally recomend with the ARMS #40 that you zero with the large aperture for the following reasons:
1) Its the default aperture when you flip it up so that is the one you'll likely use.
2) It means when you flip to the small aperture you should have a rough 300M zero

(the A2 aperture was designed so if the small aperture was zeroed at 300M the large aperture should have a rough 200M zero.  A 200M zero has an initial crossover at 50 yards with an M4 shooting M855)

If you want both apertures to have the same zero you'll need to shell out $30 for an XS Sights Same Plane Rear Aperture.  Note however the apertures are a bit bigger than the A2 apertures as they were designed to be used with the wider XS Sights front sight.

75 yards and all is good.

Quoted: I've got an ARMS 40 BUIS on my Bushmaster M4 and was curious as what the proper battle zero is for this particular sight. I got it sighted in on a 25 Meter M16 target, with the small apeture. When I switch to the large apeture it shoots about 4" low. I'm getting good groups, just wanting to know what the proper method is. Also what kind of bullet drop am I looking at, say dead on at 25M, what would my 100, 200, and 300M bullet trajectory be, using 55gr ball ammo. A couple inches hight at 100, dead on at 200 and a couple inches low at 300M? If anyone knows from experience please share, ranges and open fields are not too common up here in Wisconsin. thanks Billy

Well I sighted mine in at 50yards. Used the large apreture because I don't use the small one for anything. So I'm not sure about the drop of 4inches.

Where are you at in Wisconsin, there are plenty of ranges in this state. Hit the hometown board there is a list of ranges in the state.