Zeroing AR BUIS

I seem to recall that some people were experiencing problems with their BUIS's. The problem may be with the front sight pin. Sometimes, they need to be changed out. I wish I could remember all of the details.

I've been looking for a BUIS for the AR flat top build that I'm about to do. I decided to go with the ARMS #40L-SP. The "SP" stands for "Same Plane". (i.e. you don't have to change out the front sight.)

The description for this sight (at one of the sellers) is the following:

#40L SP- Low Profile with Same Plane aperture - Same as the #40L but the small and large peeps are on the same plane with no elevation change when switching between the two.

Here's how another seller advertises the sight:

The #40L SP is identical to the #40L but it utilizes ARMS same plane aperture system. This aperture set allows the operator to choose between large and small apertures without worrying about them being zeroed to different ranges. The small aperture can also be removed if the user desires the larger CQB aperture only.

I hope this helps a little.

I have a carbine so I also replaced the front post with the longer one from Bushmaster.

It's kind of annoying that they ship them all with the standard one for full length handguards.

The reason I ask about the BUIS is when doing the IBZ you click all the way down and use the small aperture for the intial sighting in. Then you click up to 6/3 or 8/3 and switch to the larger aperture for most shooting under 200 yards.

So I guess what I'm hearing is to sight in at 50 yards using the large aperture.

Does anyone know what range the small aperture will be set for when doing this?

I know that battlesights are not for bullseye shooting but I was curious.

Thanks for the info

If you zero at 50 YARDS, not meters.. it should keep you within 2" point of aim from 8 meters to 220 meters.

So if your sights are not on the same plane... you need to figure out how much the smaller apeture changes things. Perhaps emailing the company to ask them. They may even tell you what distance to sight in at to achieve the results expected from their sight.

From what I have read.. if you have a small and large apeture.. if the large one is setup at the 50 yards.. then it should cover you pretty well out to about 250 meters.. granted at 250 you're going to be probably 4" low. Then the smaller apeture should cover you to around 300 meters.

Looking at a ballistics chart for the ammo I have, at a 100 yard zero it's showing it dropping 2.7 inches at 200 yards, 10.9 inches at 300 yards. It's also showing it being -0.3 inches at 50 yards.

I have my buis sighted in fairly decent at 50 yards.. at 300 meters.. mine is a same plane version.. I was hitting a 12" steel plate by just holding above the target a few inches.

I think the best thing you can do, is contact the company and ask them about the sight. If it is a dual plane sight, you'll want it setup good. Like I said, everything I read says the best thing to do is sight in at 50 yards. Heck, many military sight in at only 25 yards and just make sure the bullet impace is slightly lower than the point of aim. But if you're wanting 250m with the large apeture, then 300+ with the smaller one.. I think you should ask them how they recommend zeroing it. Theirs may be a 250 and 300-400 sight.. who knows. if mine wasn't a same plane, it'd be a 250 and 300 apeture.

amishclark said:

i think the purpose behind using the large hole for initial sight-in is that it will get you on paper faster...however, it is less accurate. switching to the small hole allows you to fine tune the zero. there really should be no difference in "sight planes" between the two holes...but i'm no armorer, so i don't know.

Click to expand...

if the apetures are not on the same plane, then there is difference. Ones that are not on the same plane, the smaller hole will sit up slightly higher to have you sighted in for further distance.

The only ones that will have absolutely no difference, will be the ones that are specifically same plane apetures.

Generally on BUIS that have two apetures, the smaller hole is for the 300 m range and the larger is for 250 m and down. Granted, there won't be a HUGE difference if you sight in using the smaller apeture, but it's much harder to sight in at 300 meters than it is up close.. and since the smaller apeture isn't meant for up close.. it may throw your larger apeture off just a bit. that's not to say you can't use the smaller one up close, but the real purpose of it is for longer distance if it's not a same plane sight.

Mine is a same plane and I'm actually considering changing it. I like it, but I tend to use the larger apeture the most. I don't ever use the smaller one much. So I figure I'd be better off switching to one that isn't same plane so when I switch to the smaller, more accurate apeture, I'm sighted for longer distances without having to hold over the target so much. I'm talking 300 yards or more distance.