At a Glance:

• Fully metallic lower replacing factory plastic

• Fully assembled and upgraded with all TANDEMKROSS parts and accessories

• Drop-in ready out of the box

• Not serialized! Does not require an FFL

• Compatible with virtually ALL factory or aftermarket Ruger® Mark IV™ and Mark IV™ 22/45™ uppers

The #TANDEMIZED Cthulhu is the single best way to get the most out of your Ruger® Mark IV™ Standard or 22/45™ pistol. What was once a stripped lower that required additional parts and assembly is now ready to host your pistol’s upper right out of the box! Increase the life and durability of your pistol while also increasing its reliability and performance!

TANDEMKROSS’s Cthulhu boasts an enlarged trigger guard for large or gloved hands, a hooked trigger guard for more points of contact, and textured backstrap for improved grip and ergonomics. Additionally, the takedown button has been replaced by a single takedown screw that helps preserve the pistol’s simple takedown while reducing play between the lower and upper for a firm, secure hold. The cerakoted aluminum is also much less susceptible to damage from heat, chemicals, impact, or general wear and tear.

Since all Ruger® Mark IV™ Standard and Mark IV™ 22/45™ pistols share the same one-button takedown feature, the Cthulhu will support virtually any factory or aftermarket Ruger® Mark IV™ or Mark IV™ 22/45™ uppers. This means the Cthulhu allows you to easily turn any Ruger® Mark IV™ into a Mark IV™ 22/45™. All you need is to swap out the factory Mark IV™ magazine base pads with Mark IV™ 22/45™ base pads. TANDEMKROSS’s extended magazine bumpers perfectly fit the bill! Try either the Tomahawk or MarkPRO Magazine Bumpers that both come in packs of two.

This upgrade contains over 30 parts, components, and accessories, all from TANDEMKROSS and all fully installed, assembled, tested, and ready to go as soon as it arrives at your door. Whether for serious competition or recreational plinking, the #TANDEMIZED Cthulhu is perfect for anyone looking to improve their favorite rimfire pistol.

With the #TANDEMIZED Cthulhu you’ll receive:

• Accelerator Thumb Rest for Ruger® Mark IV™ 22/45™

• Blast Pack

• Bolt Keeper Extended Bolt Stop

• Cornerstone Safety Thumb Ledge

• Engraved Titanium Grip Screws (4-Pack)

• hiveGrip

• Cthulhu Aluminum Lower

• Rebuild Kit*

• Victory Trigger

Choose your favorite color Cthulhu and all black or all red accessories! 

Get the #TANDEMIZED Cthulhu for your Ruger® Mark IV™ or Mark IV™ 22/45™ today and make your good gun GREAT!

*The Rebuild Kit comes pre-installed. The waterproof case only comes as a separate purchase of the full Rebuild Kit.

This product is protected against mechanical failure for life by TANDEMKROSS’s Lifetime Guarantee. Learn more about our warranty and returns policies here.

INTERNATIONAL CUSTOMERS: Because the Cthulhu is a frame, it is NOT available for direct international sales.

IMPORTANT: This product complies with ATF RULING 2009-2

Any person who installs “drop in” replacement parts in or on existing, fully assembled firearms does not manufacture a firearm and does not need to be licensed as a manufacturer under the Gun Control Act. A “drop in” replacement part is one that can be installed in or on an existing, fully assembled firearm without drilling, cutting, or machining. A replacement part, whether factory original or otherwise, has the same design, function, substantially the same dimensions, and does not otherwise affect the manner in which the weapon expels a projectile by the action of an explosive. Any person who is licensed as a dealer, which includes a gunsmith, and who installs “drop in” replacement parts in or on existing, fully assembled firearms as described in this ruling does not need to be licensed as a manufacturer under the Gun Control Act. Any person who is engaged in the business of installing “drop in” replacement parts in or on existing, fully assembled firearms as described in this ruling must be licensed as a dealer, which includes a gunsmith, under the Gun Control Act.

This item is NOT considered an “80% Lower” and Complies with Rule 2021 R-05F

Grandfathers in existing classifications of frames or receivers (to include split frames or receivers) and allows them to be marked in accordance with the existing requirements.

The full definition can be found here: https://www.atf.gov/rules-and-regulations/definition-frame-or-receiver/summary

This product is NOT a serialized part.

WARNING: This product can expose you to chemicals including chromium, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov