The MAD BUIS With Ranging Aperture was originally manufactured by GG&G under a contract with Picatinny Arsenal, and although it is ammunition and weapon specific, we decided that it was time to offer it to a broader market. The MAD BUIS with Ranging Aperture has all of the same great features as the standard MAD BUIS such as its low profile, solid 4140 steel and 6061-T6 aluminum construction, solid locking detent with button release, and mil-spec finish. It has one important exception. The unique rotating multiple aperture disc has 5 apertures preset to specified distances. In particular, 0=25 and 200yds 3=300yds 4=400yds 5=500yds 6=600yds. A small window facing the shooter, as can be seen in the above photograph, provides a numerical cue as to the range. All apertures are the same diameter—-.070” diameter. The apertures have been preset using the ballistic calculations for 55 grain through 62 grain ammunition used in the AR15/M16 16" carbine length weapon.