TANDEMKROSS #TANDEMIZED Cthulhu Lower (Ruger Mark IV / Mark IV 22/45)

The Cthulhu Lower is the entire TANDEMKROSS Mark IV catalog delivered as one assembled aluminum frame. Buy it and the Victory Trigger, Cornerstone Safety Thumb Ledge, Accelerator Forward Thumb Ledge, Bolt Keeper Extended Bolt Stop, hiveGrip, Titan Extended Magazine Release, Blast Pack, and a four-pack of engraved titanium grip screws arrive already installed in a Cerakoted aluminum grip frame. Adding those parts individually to a factory lower costs most of the way to this price and takes an evening of work.

The frame itself is not just a carrier. It runs an enlarged, hooked trigger guard, a textured backstrap, and a takedown screw in place of the Mark IV's factory takedown button. At 12.40 ounces it adds weight low in the gun, which is the direction a competition rimfire wants weight to go.

Compatibility is the reason this part is interesting to owners of either frame. TANDEMKROSS states it is compatible with virtually all factory or aftermarket Ruger Mark IV and Mark IV 22/45 uppers, which means a standard Mark IV owner can move an existing upper onto it and end up with a 22/45 configuration and a 1911 grip angle. The lower is not the serialized part on a Mark IV, so it ships as a component rather than through a dealer.