Does this sit at the same hight as a fixed front sight?

Yes. Exactly perfect for the F A2 front sight post. Picatinny railed gas blocks are not the same height though and you would have to use something else. It also works on Free float rails.

Will this work on the gas blocks that are lower than the rail on the upper reciever?

No. Keep it on the rail, don't put it on the gas block if the gas block rail is lower. Your sights won't line up like they should if you do.

Do you get solid "clicks" when you adjust the elevation dial? If so, anyone know how many Clicks per MOA?

The clicks are positive. Magpul states the following in the instructions: "Each click adjusts the POI ~1.13 (1 1/8) inches at 100 meters for a typical M4-type Carbine. Your results may vary depending on your weapon and the rail position of your sights (sight radius)." 100 meters is about 109 yards, so I'm guessing it's closer to 1 inch at 100 yards.

can someone explain "co-witness" . Got a Colt ar15 and want to put a red dot on it. Everybody seems to talk about co witness?? help!

UNDERSTANDING CO-WITNESS Please post comments here. INTRO: Since this topic comes up quite a bit, I decided to put something together to help out anyone that is having a little trouble understanding the differences and to help to choose the right one. This will apply to AR-15 rifles, and more specifically to iron sights, red dot sights, and the low powered variable scopes (1x4 scopes) in tactical applications, not precision shooting. ABSOLUTE/REGULAR CO-WITNESS: This means that the reticle and the iron sights will line up. The irons and the red dot are pretty much the same height. I say pretty much because there is no such thing as "ABSOLUTE". The height for Iron sights is just under 2.6". Most of the Absolute/Regular Co-Witness mounts on the market such as Larue, ADM, Bobro, etc, are actually around 2.75", which is close enough to the iron sight height. LOWER 1/3 CO-WITNESS: This is where the iron sights appear in the lower 1/3 window/section of the optic. Most of the Lower 1/3 Co-Witness mounts on the market such as Larue, ADM, Bobro, etc, are around 3". FRONT AND REAR FLIP-UP BUIS: Front and rear flip-up BUIS is the most versatile set-up and gives you the greatest flexibility. BCM-URG-MID-14%20TR&.jpg FRONT AND REAR FIXED BUIS: These are generally the lightest, simplest, and generally the most rugged. c4cd4e0379a66e0736.jpg FIXED FRONT/FLIP-UP REAR BUIS: This is one of the most popular set-ups because most AR's come with the fixed front sight base, which is pinned and very rugged. IMG_0399002_..jpg DETERMINING THE PROPER CO-WITNESS: Now that I explained some of the terms and some of the different available options, let's determine the best height to use. If you read some of these types of threads, you will read where guys will post that the lower 1/3 co-witness is best because it allows you to keep your head in a more upright position, which is ideal for CQB type work. The upright head position, IMHO, is the correct position. Unfortunately, we are not 1-size fits all. In other words, we are not all 6'3" tall. I learned that the hard way and it cost me $200 in mounts. I have always used the absolute/regular co-witness because it was very comfortable for me. My head was in the upright position when I shoot with irons or with the Aimpoint or EOTech with an absolute/regular co-witness. So one day I purchased an Aimpoint and was talked into getting the lower 1/3 mount because my head would be in an upright position. My first range session with these lower 1/3 co-witness mounts, proved to be a huge mistake. I was no longer able to even get a cheek weld position. It was more like a chin weld position. And shooting from the prone was very painful for my neck because I had to lift up my head to obtain a proper "chin weld" position. My friend on the other hand had no problem with the lower 1/3 mounts. I'm 5'7" tall and he's 6'2" tall. So what I recommend to determine what the best height FOR YOU is without going out and spending a couple of hundred dollars on mounts is to just look through your iron sights and determine where your head is. If you look through your irons and you r head is relatively upright, then you may want to go with the absolute/regular co-witness mounts. I should mention that the sight height is more critical when using a magnifier or a regular scope. When I just use an Aimpoint or EOTech, even if it is in the lower 1/3 co-witness, it isn't that much of a problem for me because the reticle in the red dot scopes floats around. Confused yet? It gets better. What if you use fixed front and rear BUIS or a fixed front and flip-up rear BUIS? Then you to deal with another factor that doesn't exist with the flip-up front and rear BUIS. Some people, no matter how hard they try, they just can't get used to having the front sight in the way. It can be very annoying, especially with a regular 1x4 scope because the reticle just sits right on top of the front sight post. At least with a red dot, you can slightly raise your head and the reticle will clear the front sight post and not be as annoying. CONCLUSION: If you have/use the front and rear flip-up BUIS, I recommend that you just determine what height is best for you based on your head position. If you have a fixed front BUIS/Sight, you have to first determine the proper height based on your head position, and then, if you determine that you would be better off with the absolute/regular co-witness height, then you have to determine if you can put up with the front sight being in the way. PHOTOS BY QUIB Paulo Santos Weapon Review Blog SPD CrossFit SPD CrossFit FaceBook Pagehttp://www.weaponevolution.com/forum/showthread.php?2497-UNDERSTANDING-CO-WITNESShttp://www.m4carbine.net/showthread.php?17049-Explanation-of-Co-Witness

Brand	Magpul
Color	Black
Style	Front Sight
Sport	Airsoft
Item Weight	0.09 Pounds
Material	Alloy Steel
Magnification Minimum	1 x
Compatible Devices	Rifle, Shotgun
Mounting Type	Picatinny Mount
Night vision	No
Thread Type	Picatinny
Model Name	MBUS PRO Steel Backup Sights
Manufacturer	Magpul Industries Corp.
UPC	873750008370
Global Trade Identification Number	00873750008370
Item Package Dimensions L x W x H	5 x 3.07 x 1.54 inches
Package Weight	0.07 Kilograms
Item Dimensions LxWxH	4 x 3.1 x 1.3 inches
Brand Name	Magpul
Country of Origin	United States
Suggested Users	unisex-adult
Number of Items	1
Part Number	MAG275-BLK
Included Components	MBUS PRO Steel Backup Sights, Front Sight

Magpul MBUS PRO Steel Backup Sights

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