optics with back up iron sites

[calixt0]

Hello all,

I'm new to this whole ar world. I just bought a spikes tact lower with a dpms heavy barreled upper. I know what scope I am going to put on it (bsa sweet 223 3-12). The shop I bought from included BUIS and want to be able to use both... How high will the rings need to be to clear the backup sites.. pop us style.

Thanks for the help

[bohoki]

i really want to get one of these but i hear the guy is in china

http://cgi.ebay.com/Tactical-4X-32mm-Magnify-Aim-Sight-Scope-w-20mm-Mount_W0QQitemZ250394606033QQihZ015QQcategoryZ31714QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[kato4moto]

I'm not familiar with that scope, but if it's what I think it is, you'll need something like ARMS #22 quick-detach rings for it. Otherwise, you won't be able to quickly detach the scope (should it somehow fail) and employ the BUIS. Most BUIS are made to either co-witness with a red-dot or holographic type of optic or they fold down and are there as a redundant system should the primary sighting system (optic) fail. But with a typical mid- to long-range style of scope, you won't be able to use the BUIS until the scope is out of the way. At least that's the way I understand it and have set up my rifles accordingly.

[maxicon]

To choose rings vs a one-piece mount, you'll need to think about how far forward the scope will need to be mounted, which will depend on your stock and how you mount the rifle to your shoulder. As kato4moto said, you'll need a QR mount or rings to get to the iron sights quickly, or you can keep the mount tool on hand and remove the scope when you want to switch to irons. This lets you leave the irons mounted and zeroed when you put the scope back on.

Here's the Big List of AR15 one-piece mounts, including sections on rings and extended rails:

http://www.maxicon.com/guns/optics/one_piece/ar15_onepiece_mounts.htm

The ring/mount centerline height needed will depend on the folded height of the BUIS and the diameter of the scope where it will go over the BUIS.

Here's how to figure it out.

- Measure the scope's eyepiece diameter, with flip caps if you're going to use them. Butler Creek usually adds about 0.1" to the diameter. If the scope's going far enough back so the eyepiece isn't directly over the BUIS, measure the diameter where it is over the BUIS.
- Divide that by 2.
- Add that to the height of your BUIS.
This gives the minimum centerline ring/mount height that will fit with that BUIS and scope.

For example from the other direction, my Leupold VX1 4-12x40 eyepiece diameter is 1.7" with flip caps - divided by 2 gives 0.85". Mounting it in a 1" LaRue LT-104, which has a 1.41" centerline, would leave (1.41-0.85) = 0.56 as the tallest BUIS that would fit. As you can see from the list below, that leaves out many. This is one reason the Troy BUIS is so popular.

Here are some popular BUIS heights:

ARMS 40 - 0.95" folded (mine is 1.00" even)
YHM-9680 - 0.84" to the top of the windage knob, 0.74" to the top of the sight body
Matech - 0.75" folded
MI ERS - 0.75" folded
GG&G MAD - 0.625" folded
Magpul MBUS - 0.625" folded (not verified)
ARMS 40L - 0.61" folded (mine is 0.59")
Troy - 0.460" folded
MI MCTAR-SPLP - .438" folded
YHM QDS - 0.435" folded
KAC 300m - 0.315" folded

[Mississippi]

Get a REAL acog. I love my Ta31 ecos. Has back up irons on it and a red dot optic on top. 3 in 1.