#TANDEMIZED Cthulhu Lower for Ruger® Mark IV™ and Mark IV™ 22/45™


$644.99 - $669.99
(20 reviews) Write a Review
2.50 LBS
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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


Your #TANDEMIZED Kraken is built to order! This means it may require some extra time to assemble by our in-house customs shop. Please allow for as many as 3–4 weeks for full assembling and processing.


The #TANDEMIZED Kraken 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 Kraken 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 Additionally, the takedown button has been replaced by a single takedown screw that helps preserve the pistol’s simple takedown while reducing play between the lower and upper for a firm, secure hold.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 Kraken will support virtually any factory or aftermarket Ruger® Mark IV™ or Mark IV™ 22/45™ uppers. This means the Kraken 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 Kraken is perfect for anyone looking to improve their favorite rimfire pistol.


With the #TANDEMIZED Kraken you’ll receive:


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


Get the #TANDEMIZED Kraken 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 Kraken 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


20 Reviews

  • 5
    Awesome product

    Posted by Gary Petitti on 3rd Jan 2024

    I own several of these all around great product nice to get a all around package Jeff is awesome extremely helpful and knows his stuff everyone is helpful Ben Tyler all around great company to work with!

  • 5
    One of the Best Upgrades for Ruger Mark IV!

    Posted by Cody Luke on 20th Aug 2023

    I love this upgrade!It is a must for the Ruger Mark IV, makes uppers much more solid which translates into accuracy! It is well worth the money! Feels great in the hand, great trigger, great grips, a solid platform for an accurate pistol.

  • 5
    Kraken full assembled frame and red game changer compensator

    Posted by Rickey on 5th Jul 2023

    After working on my Ruger 22/45 MK IV and installing an aftermarket custom barrel, I found that I had an extra Ruger 22LR Lite barrel laying around. Reading all the information, I found that these barrels were just as accurate as many of the aftermarket barrels. I then noticed that Tandemkross had come out with a fully assembled "Kraken" frame. At first it was out of stock. It soon became available, and I placed an order for a red frame and red game changer compensator. I installed both and have since gone to the range to sight them in. Like all products from Tandemkross, they work prefectly! Products and service from Tandemkross are exceptional!

  • 5

    Posted by Alex on 6th Nov 2022

    Exactly what I had hoped... a competition ready frame, out of a box...the balance is perfect and the trigger pull is light with a nice little take-up... and that trigger guard! Very handsome

  • 5
    Tandemized Kraken is a Winner

    Posted by John on 29th Oct 2022

    This lower is outstanding! Every item on it is superb. Most important, it makes shooting so much better. The trigger is about 1.9 lbs! WOW! Buttons are a litter larger and very easy to reach. All in all, this is a superb lower for the Ruger Mark IV 22/45 Lite.

  • 5

    Posted by Gilberto on 13th Aug 2022

    If you want quality put together with the best service crew ever, you MUST have a Kraken.

  • 5
    Kraken lower

    Posted by Anthony Seta on 6th Jul 2022

    Without a doubt, the Tandemkross Team does make guns great and I will take one step further, they are outstanding. I took it the range last week to sight it in and everyone was in amazed with how the gun felt in their hand and how well it shot. Thank you for the Kraken. I am very proud to shoot it and very honored that it is part of my collection.

  • 5

    Posted by Alan Nelder on 27th Jun 2022

    Just received the Kraken. It is wonderful! I mounted a Volquartsen barrel and bolt to make a great pistol. I had a couple questions and Tyler answered them immediately. I ve been dealing with Tandemkross for many years. It has been a real joy!

  • 5
    KRAKEN lower

    Posted by Scott on 18th Jun 2022

    I received the Kraken Lower a month ago and finally after a brief illness got to shoot it at a Steel Challenge match today (6-18-22). I loved it. In three of five stations I was able to improve from class c to class b. The trigger is by far the best I ve ever used and the quality and craftsmanship is fantastic. I would recommend if your looking to upgrade you Ruger Mark IV.