From Trijicon

An extremely rugged and durable closed emitter optic which meets the demanding standards for military and law enforcement applications. The Trijicon RCR^®represents the next evolution of the Trijicon RMR® and is designed to be as durable as the legendary Trijicon ACOG®, while also improving precision and accuracy with any style or caliber of firearm in any type of environment. The RCR can withstand direct impacts and survive in the harshest environments, while still providing enhanced accuracy and an excellent field of view. The RCR does this while not requiring additional or new plates to be used as it works with the current RMR bolt pattern and direct mounts without the use of a dovetail.