Review: ZRODelta Modulus

posted on June 22, 2020
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Modularity seems to be the next coming trend in firearms design. Modularity means that key components used in assembly can be removed and replaced with other components; effectively yielding a different product. Many makers are offering rifles with barrels and stocks that can quickly and easily be changed.

Semi-automatic pistols are not immune and there are now several modular handguns on the market. Some of these pistols are new designs while others are adaptations of existing ones. An example of the latter is a pistol from ZRODelta called the Modulus.


The Modulus is a 9mm handgun based on the Glock G19 Gen 3 but with some key differences. Most obvious is the frame. Rather than being molded from polymer, the Modulus frame is constructed from aluminum. The central frame section is machined to accept different front and rear grip inserts as well as different length magazine well extensions.

The dust cover, or railed section, in front of the trigger guard is also removable. It can be swapped out with different dust covers thereby shortening or lengthening the frame in relation to the slide being used. Internally, the frame uses mostly G19 Gen 3 pattern parts although the magazine release is more like Glock’s later Gen 4 piece. Being based on the Gen 4, the magazine release can be removed and switched to protrude on either the right or left side of the pistol.


Modulus slides are available in three lengths. These are called “Compact,” “Duty” and “Extended.” All three slides feature front and rear cocking serrations and come outfitted with black steel sights. Slides are machined to accept a red dot optic and ship with a cover plate installed.

ZRODelta sells a number of adapter plates for the more popular pistol red dots on the market. Barrels are available in 4.01", 4.58" and 5.31" formats that correspond to the aforementioned slide lengths. Being based on the Glock 19, these barrels are G19 pattern at the lower camming surface.


As shipped, the Modulus is configured in the Compact format and is available as a stand-alone handgun or in a complete set called the Deploy Kit. The Deploy Kit comes in a zippered padded bag that includes the Duty and Extended complete slide assemblies as well as all of the available grip and magazine well inserts.

Hand tools needed for conversion are included in the kit as are magazines of the correct lengths. Those wishing to buy the Modulus pistol, and only a few of the available accessories, can go that route as well. All the Modulus conversion pieces are available à la carte from ZRODelta.


What does the Modulus offer that can’t be had from similar Glock-pattern pistols? While there are some aftermarket “Glock 19L” slides that allow a shooter to convert a compact pistol into something with a longer barrel and sight radius, the Modulus goes one step further and also lets the shooter choose the frame length most appropriate to the task at hand.

In theory, one Modulus pistol could be used for concealed carry, open holster or duty carry and competition by changing out the slide and swapping in the necessary magazine wells. Additionally this one pistol could be configured into an unusual combination of parts such as the Compact magazine well with the Duty or even the Extended slide formats. One pistol to buy, one trigger to learn, one manual of arms to become familiar with. The idea has merit. 


Changing parts on the Modulus is fairly straightforward and intuitive. Once the pistol is unloaded and verified clear, the slide is removed via the standard Glock method of de-cocking the pistol and pulling down on the slide lock tabs. Next, remove the dust cover retention screws and install the appropriate dust cover to the frame. The frame’s magazine well is changed by removing a bolt below the pistol’s back strap and unhooking the magazine well from the frame.

With the magazine well off the pistol, the front and rear inserts can be slid off and swapped out for a size or style that feels best to the shooter. One caveat to removing the back strap. In order to get this piece off, the user will need to first push out the trigger housing pin located at the frame’s rear. Once the frame is assembled in the desired size, slide the corresponding slide on until it locks in place.


The full-length grip format was used for testing with only the slides and appropriate dust covers being changed as needed. Range testing consisted of running some basic drills from the holster with and without a light attached.

The Modulus fit fine in an old leather Bianchi holster and worked properly in a Safariland ALS holster made for the Glock 19 with weapon mounted flashlight. The Modulus is quite close in size and appearance to the Glock but is different in some areas cosmetically and dimensionally. This may affect fitment in some brands/types of holsters.

Is the modular firearm idea really new? Dan Wesson long ago made a double-action revolver that came in a kit that included multiple barrels in various lengths. The Thompson Center Contender is another example. Built on a break-open receiver, the Contender is not only available in multiple barrel lengths but also in multiple calibers.


During the Vietnam War, U.S. Navy Seals fielded a machine gun known as the Stoner 63. This firearm used a central receiver and could be fielded as a squad automatic rifle, infantry rifle or belt fed machine gun by changing the barrel and related parts.

All these examples allow the shooter to configure the firearm to meet a specific requirement with little or no armorer support and a minimum of tools. So the modular firearm concept has been around awhile but it doesn’t seem to have really caught on until recently.

Have it your way. That doesn’t just apply to hamburgers. 


Base Modulus Compact Pistol Specifications
MANUFACTURER: ZRODelta, 100 Beiersdorf Dr, Connelly Springs, NC 28612
MODEL: Modulus
CALIBER: 9mm
BARREL: 4.01” 1:10" twist
SLIDE: 17-4PH stainless steel, black nitride treated         
FRAME: 7075 Aluminum
TRIGGER: 6.75 pounds measured
WEIGHT: 23.5 ounces      
MSRP: $919.00 

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