This is a Leupold Mount known as the DeltaPoint Pro, model 177154.
Most people think of the DeltaPoint Pro as a pistol sight" but it's just as capable on an AR platform as it is on a handgun. The DP Pro AR mount brings the red dot to just the right height without adding a ton of weight or bulk. It's ideal for AR pistols for lightweight builds where every ounce matters.
Features:
Puts the DP Pro to the right height for AR's
Fits any Picatinny rail
Precision machined from aerospace-grade aluminum
Made in the USA