The TANDEMKROSS Cthulhu lower gives Ruger Mark IV 22/45 owners a different path than upgrading the factory polymer lower one part at a time. It comes assembled with the trigger, safety, thumb rest, slide lock, magazine release, and other controls already installed.
Earlier versions of this product used the TANDEMKROSS Kraken lower name. My original red build dates back to that version. My newer FDE and green builds use the current TANDEMKROSS Cthulhu lower. The name changed, but the basic idea stayed the same: start with a premium aluminum Ruger Mark IV 22/45 lower, then choose the upper, bolt, sights, optic, and muzzle device that fit the pistol you want to build.
After years with the original Kraken and two newer Cthulhu lowers, I now have three distinct pistols built around the same concept. Each one has a different role. Together, they show that there is no single correct way to complete a TANDEMKROSS Cthulhu lower build. This is not a parts wish list. These are three Cthulhu/Kraken lower builds I actually own and shoot.
For readers comparing Ruger Mark IV 22/45 build options, the TANDEMKROSS Cthulhu lower makes sense as a premium foundation. It already includes the major controls, leaves the factory Ruger lower intact, and works with a factory Ruger Lite upper, a lightweight Pac-Lite upper, or a short Mamba LLV upper.
Anyone considering one can check the current Cthulhu lower options and pricing directly from TANDEMKROSS.
Why Build Around a TANDEMKROSS Cthulhu Lower?
I already knew many of the individual TANDEMKROSS controls before I bought the original Kraken. Another Ruger Mark IV had an upgraded trigger, safety, thumb rest, and related parts. The lower itself was the real question. I wanted to know whether the aluminum frame would make the pistol feel different.
That difference is hard to measure with numbers. I cannot show data proving that I shoot faster or more accurately with the Kraken or Cthulhu lower. After shooting the original Kraken for a while, though, I developed a clear preference for it over the factory polymer lower.
What the Cthulhu Lower Changes
TANDEMKROSS explains the design well. The enlarged trigger guard gives more room for large or gloved hands. Its hooked front adds another point of contact. The textured backstrap also improves the way the pistol sits in the hand. Compared with the factory polymer frame, the Cerakoted aluminum lower feels more substantial.
The takedown system changes, too. TANDEMKROSS replaces Ruger’s push-button takedown with a screw that locks the upper and lower together. Losing the push button may sound like a downside, but it has not been a problem for me. I keep the wrench handy, and I rarely need to separate the upper and lower away from home.
More importantly, the screw has never loosened during use. The upper-to-lower fit has always remained solid.
What Still Needs to Be Chosen
There is little reason to start changing parts inside the current TANDEMKROSS Cthulhu lower. It already includes the trigger, safety, thumb rest, slide lock, and magazine release. Replacing those parts mostly means chasing diminishing returns.
The more meaningful decisions involve the parts above and in front of the lower. The upper, bolt, sights, optic, and muzzle device do more to define the finished pistol.
The names started as a joke after someone on Reddit compared the red and FDE builds to peanut butter and jelly. The green lower really pops in direct sunlight, so Ca$h Money seemed like the obvious name.
Jelly: The Original TANDEMKROSS Kraken Lower Build
My red pistol, which I call Jelly, uses the original TANDEMKROSS Kraken lower. Other than the Ruger Lite upper, the major components are TANDEMKROSS parts.
The build includes:
- Original red TANDEMKROSS Kraken lower
- Red Ruger Mark IV Lite upper
- TANDEMKROSS Krossfire bolt
- TANDEMKROSS Tempest grips and magwell
- TANDEMKROSS Eagle Eye fiber-optic sights
- TANDEMKROSS Shadow optic mount
- Viridian RFX15 green dot
- TANDEMKROSS Game Changer compensator
This is the fastest-shooting of the three pistols. The grips, thumb rest, safety ledge, optic, and fiber-optic sights all support the same goal: point naturally and get on target quickly.
The Eagle Eye sights work with the optic setup and give me a bright, familiar reference when the dot is not immediately visible. That helps because astigmatism can make red dots bloom. With this setup, I can use whichever sight picture looks clearer at the time.
The Game Changer compensator normally stays on the barrel. Jelly can be used with my suppressors, but it is the least suppressed of the three builds. I may not consciously notice an extra six ounces when holding a .22 pistol, but that weight at the muzzle makes a difference when moving quickly from target to target.
The compensator redirects gas and reduces the small amount of muzzle movement produced by a .22 LR pistol. I have not done controlled testing to quantify that effect. For this build, the bigger benefit is balance. The compensator keeps the muzzle light and preserves the quick handling that Jelly was built around.
Can You Use a Factory Ruger Lite Upper With the TANDEMKROSS Cthulhu Lower?
Jelly demonstrates that buying the TANDEMKROSS Cthulhu lower does not always mean spending more money on an aftermarket upper.
The factory Ruger Lite upper is an excellent match on its own. Someone who already owns a Ruger Mark IV 22/45 Lite can add the Cthulhu lower and make a substantial change to the way the pistol feels without replacing the upper.
That may be the most practical upgrade path. Buy the Lite first, then add the Cthulhu lower. If you replace the upper later, you still have the factory polymer lower. Instead of ending up with one heavily modified pistol and a pile of unused parts, you have the foundation for two complete pistols.
My earlier articles on building the original TANDEMKROSS Kraken, the Krossfire Ruger Mark IV bolt, and the Eagle Eye fiber-optic sights provide more detail on the individual components used in this build.
Peanut Butter: FDE TANDEMKROSS Cthulhu Build
The second pistol is Peanut Butter, as in “Tactical Peanut Butter.” This build started when I acquired another upper and found myself with more uppers than lowers. Around the same time, TANDEMKROSS announced the FDE Cthulhu lower.
The timing made sense, and the FDE version seemed like a good foundation for a field-oriented pistol. In this case, “field pistol” does not mean that I actually get to carry it in a holster while hiking. I have not found a holster that fits the Cthulhu lower with its thumb rest, although I have not looked especially hard.
Instead, Peanut Butter gets used while walking around a large open shooting area with a mountain as a backstop. It is the pistol I use for more measured shots at broken clays, golf balls, empty cans, and other small targets scattered across the area.
The build includes:
- FDE TANDEMKROSS Cthulhu lower as supplied by TANDEMKROSS
- Six-inch Tactical Solutions Pac-Lite upper
- OEM Ruger bolt
- TANDEMKROSS Sentinel Guide Rod
- TANDEMKROSS Eagle’s Talon Extractor
- Vortex Venom 3 MOA red dot
- Lobos Industries low-profile optic mount
The Pac-Lite upper fits this role well because it is long, light, threaded, and built around a relatively simple round tube. Unlike the Ruger Lite upper, it does not have the same collection of open cuts and exposed edges. In my opinion, that makes it a better choice for a pistol that may get carried in a pack or used around dirt, rocks, and brush. There are fewer openings to collect debris and fewer edges to attract scratches and scrapes.
This six-inch upper does not feel awkward or noticeably change the balance. Before adding the optic, the longer sight radius helped with iron sights. The Vortex Venom eventually replaced them, and I chose the 3 MOA version over the 6 MOA model because this pistol is used for more precise aiming rather than maximum speed.
The Pac-Lite IV article covers the upper in more detail.
TANDEMKROSS Cthulhu With an OEM Ruger Bolt
Peanut Butter still uses an OEM Ruger bolt rather than a complete aftermarket assembly. I added a TANDEMKROSS Sentinel Guide Rod and Eagle’s Talon Extractor.
I no longer recall whether I installed those parts because the bolt was purchased stripped or simply as preventative upgrades. Either way, I did not need to replace the entire bolt. This build shows that an OEM bolt can remain part of a premium Cthulhu configuration while still benefiting from upgraded cycling and extraction components.
TANDEMKROSS Cthulhu Optic Mount Choices
The Lobos optic mount is another good example of a build choice involving a tradeoff.
It sits low and is probably the best-looking Ruger Mark IV optic mount available. The Vortex Venom appears integrated into the upper rather than perched on top of a rail. The downside is that the mount fits a single optic footprint, while the TANDEMKROSS Shadow Mount accommodates multiple footprints.
That difference does not need to become a separate debate. The Lobos mount made sense because I already knew which optic I wanted to use. Someone who expects to change optics later may prefer the added flexibility of the TANDEMKROSS mount.
Peanut Butter usually wears a thread protector, but it also gets regular use with the Tactical Solutions Axiom suppressor. The suppressor changes the sound, not the pistol’s role. I still use it for the same slower, deliberate shooting.
Ca$h Money: Suppressed TANDEMKROSS Cthulhu Build
The green pistol is Ca$h Money. I acquired the upper first, which left me with four uppers and three lowers. Since the Mamba LLV was already a premium upper, I wanted to pair it with a premium lower rather than use another factory polymer frame.
The green TANDEMKROSS Cthulhu with black accessories was the obvious choice. I have not changed anything on the lower since it arrived from TANDEMKROSS. It is already exactly what I wanted, and the green-and-black combination looks about 100 times better in person than it does in the product photos.
The build includes:
- Green TANDEMKROSS Cthulhu lower with black accessories
- Three-inch Volquartsen Mamba LLV upper
- Volquartsen Competition Bolt
- Volquartsen fiber-optic sights supplied with the upper
- SilencerCo Sparrow suppressor
Ca$h Money does not use an optic. The quality fiber-optic sights supplied with the Mamba LLV are more than adequate for what this pistol was built to do.
TANDEMKROSS Cthulhu Built for Suppressed Shooting
The three-inch barrel keeps the pistol compact with a suppressor installed. It also keeps ordinary bulk ammunition subsonic.
I tested several brands of bulk .22 LR through this exact pistol using an Athlon chronograph. The highest velocity recorded was only 1,054 feet per second. That result matters because dedicated subsonic ammunition can be more expensive or harder to find. Ca$h Money can remain quiet with Walmart’s Federal bulk rather than depending on a steady supply of CCI subsonic ammunition.
The SilencerCo Sparrow is dedicated to this pistol. Compared with the Tactical Solutions Axiom, the Sparrow is almost an inch shorter while only adding about half an ounce. The shorter suppressor works well with the three-inch upper and helps preserve the compact overall length.
The Sparrow also has an excellent reputation and offers a lot of value for its relatively modest price. I still shoot plenty of 9mm, so every .22 pistol feels light by comparison. I do not really notice the suppressor’s weight when shooting Ca$h Money.
Plenty of Accuracy for Quiet Plinking
The short barrel has not created any practical accuracy or reliability problems.
At our shooting area, the fire department left a long horizontal water tank near the 200-yard line. It is roughly the diameter of a standard propane cylinder used for a gas grill, although considerably longer. I can hit it with this three-inch pistol and its fiber-optic sights.
I would not call Ca$h Money a precision pistol. It does, however, provide plenty of practical accuracy for quiet plinking. It could also be used for hunting or pest control, although less expensive options certainly exist for those roles.
That is the main tradeoff. This is an expensive pistol for what is essentially a dedicated quiet plinker. I would not change it, though. It was built with intent, and every major component supports the role.
Three TANDEMKROSS Cthulhu Lower Builds With Different Roles
None of these pistols gets noticeably more use than the others. Each one has a different job.
- Jelly is for shooting fast and moving quickly between targets.
- Peanut Butter is for more measured shots at smaller targets.
- Ca$h Money is for compact, suppressed fun.
The TANDEMKROSS Cthulhu lower does not lock the owner into one style of Ruger Mark IV build.
Jelly shows that a factory Ruger Lite upper can be an excellent match. Peanut Butter shows how the same lower can anchor a longer, lightweight, optic-equipped outdoor plinker. Ca$h Money shows how far the concept can go with a short premium upper, competition bolt, iron sights, and dedicated suppressor.
In each case, the TANDEMKROSS Cthulhu lower provides the same premium foundation. The upper, bolt, sights, optic, and muzzle device determine how the completed pistol gets used.
TANDEMKROSS Cthulhu Lower FAQ
Is the TANDEMKROSS Cthulhu lower the same as the Kraken lower?
The current product sells as the TANDEMKROSS Cthulhu lower. Earlier versions used the Kraken name. My red build uses the original Kraken lower, while the FDE and green builds use the newer Cthulhu lower. Krakens were originally anodized. Cthulhu lowers are Cerakoted.
Can I use a Ruger Mark IV Lite upper with the TANDEMKROSS Cthulhu lower?
Yes. A factory Ruger Mark IV 22/45 Lite upper is an excellent match for the TANDEMKROSS Cthulhu lower. That is the setup used on Jelly, my red Kraken build, and it shows that an aftermarket upper is not required.
Do I need an aftermarket bolt for a TANDEMKROSS Cthulhu lower build?
Not necessarily. Jelly uses a TANDEMKROSS Krossfire bolt, Ca$h Money uses a Volquartsen Competition Bolt, and Peanut Butter still uses an OEM Ruger bolt with upgraded TANDEMKROSS internal parts. The right bolt depends on the build.
What is the best Cthulhu lower build option?
There is no single best option. A factory Ruger Lite upper makes sense for a practical upgrade, a Pac-Lite upper works well for a lightweight outdoor plinker, and a short Mamba LLV upper is a strong choice for a compact suppressed pistol.
Final Thoughts on the TANDEMKROSS Cthulhu Lower
After years with the original Kraken lower and two newer Cthulhu lowers, I have a clear preference for them over the factory Ruger Mark IV 22/45 polymer lower. The difference is not something I can track on a spreadsheet, but it is obvious once I start shooting. The pistol feels more refined, the upper and lower lock together solidly, and the overall experience is simply better.
The price is significant, but the current lower arrives with nearly every control most owners would otherwise add individually. More importantly, buying a complete Cthulhu lower leaves the factory Ruger lower intact. That gives the owner more flexibility and can eventually turn an upper upgrade into a second complete pistol.
The simplest path is still one of the best: start with a Ruger Mark IV 22/45 Lite, then add the TANDEMKROSS Cthulhu lower. The factory upper works extremely well, and there is no requirement to replace it. Anyone starting from scratch with a specific role and a larger budget can choose an aftermarket upper from the beginning.
Either way, the lower is the foundation. The three builds shown here are not the only possibilities. They are examples of what can happen when the same premium Ruger Mark IV 22/45 lower gets configured for speed, deliberate shooting, or suppressed use.
Visit TANDEMKROSS to see the current Cthulhu lower colors, availability, and pricing.