The Receivers (Lower and Upper)

The basic design of the receivers for this weapon are here:


The lower receiver acts as a container that holds the various important parts of the firing mechanism (hammer to strike the firing pin (if applicable),  the Bolt bolt (to provide a temporary wedge to the end of the barrel during firing; a recoil spring mechanism to slow the bolt; an ejector so that the cartridge will be ejected and a fresh cartridge fed smoothly into the chamber to be fired, repeating the cycle. Several excellent designs exist for reliable subguns, ranging from complex locking recoil designs to gas operated and buffered designs to simple blowback designs. While all had advantages, the blowback design is the most robust, using simple physics of its massive bolt to contain the cartridge for just enough time to allow the bullet to exit the barrel before pulling cartridge free of the chamber. One of the criticisms of this project was that I was “reinventing the wheel” rather than coming up with something new like the Swiss KRISS or the Brugger & Thomet MP-9. Nothing could be further from the truth. While the KRISS or the MP-9 are designs with innovations, they were designed as pistols first with added capabilities. The Max-10 Katana is designed around the cartridge and to be a carbine above all, using the best available design features as well as throwing away those that are unnecessary. For example the KRISS system could have been incorporated into the design, but slow motion studies showed that a simple muzzle brake could reduce muzzle rise to zero. In fact the first designs were shown to be venting too much gas, as the barrel was actually being depressed on each shot by the action of the gas. Therefore a radical redesign to incorporate an unnecessary but advanced mechanism was completely eliminated.

After looking at well over 30 successful designs ranging from the English Sten gun to the Russian PPs43 to the American AR-15 9mm clones (which can be found in both gas operated and recoil operated versions) to the Thompson gun to the Israel UZI to the Ruger 44 mag carbine, I found the best design of all. Rather than scaling down a rifle (the usual approach) or attempting to bring a modern 9mm design upward I selected a .45 machine pistol and scaled it up based on Pressure, while retaining its massive and simple internals designed to handle a larger cartridge. The receiver I chose is the modern version of the Mac-10 produced by Masterpiece Arms. I turned it into a carbine by adding only those items needed to scale the design (i.e. a fore-grip, a flattop rail for optics mounting that attached to the upper receiver with a barrel rigidly screwed into the upper receiver making them one piece, a bolt massive enough to take the 10mm as a blowback, a simple buttstock that folded but was strong enough to be used as a CQB weapon and would also allow firing of the weapon while folded). The fore-end was a piece from Lage Machinery, who makes a nice fore-grip setup for the MAC-10 as well as massive bolt addition by Lage to increase bolt mass. Lage makes the bolt addition as a way of reducing the high cycle rate of the full auto MAC-10, not a concern of ours but a fortuitous development. While the bolt addition slows cycling, it also increases dwell time, allowing a higher pressure cartridge to fire its bullet and pressures to safely drop before extracting the case. The Lage fore-end allows for a two handed grip much like a rifle, completely changing the “personality” of this weapon. MPA already has modified the weapon for side cocking on the left side (which is good for both Left and Right handed operators) freeing up the upper part of the receiver to use with a rail for sight mounting. Also gone is the horrible “front strap” which gives every owner nightmares of shooting his own hand.

"Pistol" is completely transformed by Lage options.

“Pistol” is completely transformed by Lage options.

Massive bolt addition used to harness the 10mm in blowback

Massive bolt addition used to harness the 10mm in blowback

A custom barrel in 10mm with exact modifications necessary to adapt it to the MAC-10 upper receiver plus some special fitting gave me the support the cartridge needed to work effectively. In the MAC-10 system, the bolt both encloses the cartridge as well as supports it from the rear. By gently notching the barrel just enough to clear the extractor, I got full case support as well as never having the extractor “ride up” on the barrel at all. Once the extractor clipped the case rim, it stayed tight till the ejector kicked it free.


This is weapon before mods to feed ramp and chamber. Notice distance to chamber mouth from magazine. The 10mm, a long cartridge like the 9mm, feeds beautifully from the grease guns magazines due to its length and the length of the feed lips of the Magazines. As it is a blowback, the extractor is largely unnecessary as gas pressure pushed the case from the chamber. The MPA stock extractor is retained so as to adjust the ejection in a predictable way for left handed shooters. If ejection is angled too far back, a case deflector as well can be added.

Design Flaws:

One of the known major issues of the “Mac” series was a nasty tendency of the weapon to “Trigger Slap” the firer. Trigger slap is a phenomenon present on a number of gun designs, but most commonly encountered on semi-automatic AK-47, AK-74 and MAC-10 clones. In some of these guns the trigger “slaps” against the operators finger when it resets. It can range from a mild annoyance to bad enough to numb or hurt the operators finger. In the case of MAC-10 clones, it is the result of the BATFE rules requiring them to fire from a closed bolt. This design problem was not as much of a issue with the original open bolt MAC-10 machine pistols. Masterpiece Arms has developed a hammer/disconnect that completely eliminates trigger slap.


This leaves the functional and simple firing control group alone while eliminating a really bad problem in the basic design.

The upper receiver is a simple box section that fits into the lower and is connected by a pin at the front. Normally a two piece pin, in this case I have replaced it with a “captured ball” type pin to prevent it walking out from vibration. The barrel is held into the upper by being screwed in, but only requires simple tools to replace.

Into this lower is welded a magazine tube which doubles as a hand-grip. A slot is cut out in the lower for the trigger to protrude. The trigger guard is simple sheet metal but the front is used as part of the feed ramp. While the trigger guard design is inexpensive, it is a pain to adjust once installed. I found a simple CNC part would replace the trigger guard for this function and serves much more reliably, though the trigger guard would serve fine if shaped properly and supported by good welds. The Masterpiece Arms welds are excellent. The lower receiver is stamped with the serial number (and it is written beneath the finish at the rear) for Federal Identification. The magazine retainer can be difficult to manipulated but several manufacturers produce different latches that are easy to use, both left handed and right handed (Lage) or Universal (U.S. Machinegun) or Extended (Mac-Parts) units are purchasable.

The sights are a joke. I mean so bad that there was never any question of simply machining them off and starting over. The rear “sight” is simply a hole drilled in a tongue of steel that sticks up at the back. The front sight is welded on the upper receiver. No adjustment is possible with either. Happily a rail with adjustable sights is included with the Lage upper or a full length rail without sights. As the men using this weapon will want to be customize it, I would recommend the full length rail.


The Mac-10/11 family of weapons with the Lage upper has been winning national and international titles in the subgun category.  Speed of deployment, balance, hits on target against a clock, accuracy and a dead reliable system combine to win over such designs as HK, AR-based subguns, and the historic designs. Using the Lage design, you hit faster, more, better and with greater accuracy than any other sub-gun in the world. With the modification to 10mm, you now hit with maximum power as well! As a PDW, the Anduril has no comparison. Faster than an HK subgun, more reliable, shooting max power/max Accuracy ammo with a fixed barrel/rail combo and a “hand finds hand” model receiver of proven, simple design, the LongSword represents the best of the personal weapons.



Add: Magazine adjustment
Add: Grip mods
Add: Finishing touches.

ALL ITEMS DESCRIBED and their sources will be placed on a “Sources” page so that “Katanas” can be duplicated.

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