I wanted to write up a review comparing and contrasting two of the major pistol-caliber rifle options on the market today, the Kel Tec Sub-2000 and the MechTech upper receiver. I've owned both (separately) and had a hard time finding a direct, head-to-head comparison of the two. I hope this helps others make a decision! First, the Kel Tec Sub-2000 (hereafter referred to as the S2K). The S2K is offered in 2 calibers and multiple models, designed to accept handgun magazine from a variety of manufacturers. S2K's come in 9mm models, accepting magazines from Glock 17, Glock 19, S&W 59, Beretta 92 and SIG 226 handguns and in .40 S&W models with magazine wells designed for Glock 22, Glock 23, S&W 4006, Beretta 96 and SIG 226 magazines. The great thing about this, obviously, is the ability to interchange not just ammunition but also magazines with your sidearm. Another innovative feature of the S2K is that it folds in half. When folded it is inoperable and can be locked in the folded position, providing adherence to restrictive gun laws in some states that otherwise don't allow rifles to collapse or change size. Folded size is 16” x 7”, with a little over an inch of thickness. The folded position leaves the bolt face and barrel exposed and the front sight tower latched into the buttstock (locking being optional). The rear sight is a non-adjustable peep, basically a hole drilled in a piece of plastic. The front sight is a hooded, neon-colored blade of translucent plastic which is adjustable vertically by loosening a set screw and moving the blade. Lateral adjustment is provided by the turning the same set screw. Kel Tec does offer front rails and the option of a swing-away sight rail that still allows for full use of the folding feature, albeit with a sight hanging off the side of the folded gun. Controls are unique with the bolt being operated by a handle hanging under the buffer tube between the receiver and the shoulder stock. It can be locked open by pulling the bolt back and sliding it sideways into a notch. There is no “last round hold open” feature on the S2K. There is a manual safety located above the pistol grip; there is no magazine safety. Kel Tec prohibits the use of aluminum cased ammunition in the S2K. I bought my S2K (a 9mm Glock 17 model) from Wild Bill's in Molalla a few years ago. It was an impulse purchase, I had heard about the guns and when I happened to see one I snatched it up. Note: Kel Tec ships all their S2K's with 10-round, single-stack magazines. It was a good gun, and I purchased a Glock 19 to go along with it. Research showed that a Glock 19 model of the S2K existed but was hard to find, so I wrote the factory regarding a conversion. They replied that they could do the work for free if I shipped the gun back to them, or I could have a local gunsmith do it; I elected to have the modification done locally. It was easy really, the only modification required was shortening the grip 1/2”~ to accommodate the shorter magazine. It still accepted the standard Glock 17 magazine and did well with the 33 round mags as well. Overall I thought it was a good gun. I added a stock extension (available from Kel Tec) for a little longer LOP and put the factory's sling on it, although I never could get the sling adjusted to sit right for me. The stock is otherwise fixed in length. The sights were a little chintzy and hard to adjust with precision, but it was still a fun gun to shoot. I never really tried grouping it, and the results probably would have been less than the gun is really capable of (my rifle shooting has progressed immensely since then, thanks Appleseed!). I liked the ability to swap magazines with my carry gun as well. In the end, I sold it to finance a suppressor. My Sub-2000: The MechTech Upper The MechTech upper is not technically a firearm, but rather a firearm accessory. It is basically a pistol-caliber rifle upper that accepts a pistol lower to make a complete, functioning rifle. That means it can be shipped directly to your home without having to go through an FFL. They currently make multiple models designed to accept frames from Glocks (compact and full sized) to fire 9mm, .40 S&W, 10mm and .45 ACP. They also make models in 9mm, .380 super, .40 S&W, 460 Rowland and .45 ACP designed to work with 1911 frames and the appropriate magazines. Multiple stock options are available, including a telescoping wire-framed stock, a fixed stock, an M4-style adjustable stock and an M4-style stock mount that allows you to screw in your own AR buffer tube and slide on the stock of your choice. There are multiple foreend, rail and sight options available as well. When you order your upper form the factory they will install everything you've requested for no additional charge and ship it to you fully assembled (less the pistol frame). The version I have is a 9mm model designed to accept a compact Glock frame. Just as the frames on the Glock 19, 23 and 32 are functionally the same (with different slides and barrels), any of these three compact Glock frames will fit regardless of the upper's caliber. I bought mine used off NWFA with the telescoping wire stock, a single sight rail on the “receiver” and the “muzzle decoration” as MechTech calls it. It's not really a muzzle brake or a flash hider, it's just a decorative thing that is attached to the barrel via a sweat fit at the factory. Removal requires it to be turned off on a lathe; you can also order the upper without it. The bolt is operated from the left side, with a handle sticking out about 3/4”. The bolt can be locked open by pulling fully rearward and pushing the handle in roughly 1/8”; it is released by pulling the handle out. Like the Kel Tec the bolt is not held open on the last shot. There is no manual safety, although any manual safety installed on the pistol frame (aftermarket Glock or standard 1911) should work with the upper. They say that extended 1911 safeties won't work with the MechTech upper, as the extended length won't allow full engagement. Assembly is easy-ish. The Glock model requires the use of a “Glockblock”, a small machined piece of metal that sits on the pistol frame just forward of the magazine well (the 1911 version requires a similar "Parablock"). The latest versions have a small magnet to hold it in position during assembly; once assembled the block is captured between the frame and upper. It acts as an intermediate feed ramp between the magazine and the upper, and it seems to do the job well. With the Glockblock in place on the pistol frame the four rail tabs are engaged into mating spots on the upper and the pistol frame is pushed forward against a rubber bumper, compressing it until the frame's takedown lever is fully engaged (similar to putting a Glock pistol back together), locking everything together. Disassembly is the reverse; push the pistol frame forward against the upper, compressing the bumper enough to allow the takedown lever to be slid downward so that the frame can be slid backwards off the upper. Quite a bit of force is required for either operation, and the factory includes a rubber cane-tip to put over the muzzle, allowing you to put the upper muzzle-down and push against the floor for assembly or disassembly without damaging anything. No sights are included unless you order them, and since mine came with a single short rail I decided to mount an inexpensive red dot (a Millett from Bi-Mart). It shoots well, the trigger reset is similar to a standard Glock pistol and it is accurate enough at 50 yards. I was able to maintain 2-3” groups with reloads the last time I was out. Side note: when I bought the MechTech the rubber bumper had been shaved down to roughly 60% thickness by one or more previous owners, making assembly and disassembly easier. In use I found that the lower wasn't properly engaging the striker/firing pin on the upper when I pulled the trigger, leading it to not fire most of the time. I suspected the carved-down bumper to be the culprit, so for diagnostic purposes I shimmed it a bit with some fiberboard and it worked great. I wrote Mech-Tech and explained the situation and they sent me a free bumper! Replacement was easy, I shaved the old one off the foreend and glued the new one back on with gelled CA; operation has been flawless through 150 rounds. They were also nice enough to send me a new-style latch for the telescoping stock that allowed actuation by pushing up from the bottom rather than pulling up from the top. Overall, I prefer the MechTech over the Kel Tec. Although it's heavier, it's also more robust and feels more like a rifle should than the S2K. I can't really explain what that means, but most of you will understand that intangible sort of feel that comes from shooting a stable long weapon. Additionally, the MechTech with the telescoping stock can be shortened to an overall length of 25” (26 3/4” with the muzzle dec), making for a compact package that still functions as a firearm. I wasn't really impressed with the sights on the S2K, and all the aftermarket options interfered with the folding feature (either by not allowing it to fold or by handing off the side of the folded gun). I admit that I'm a little bit leery of a rifle with no manual safety. My plans include purchasing a dedicated Glock frame to use with the upper (they're available on Gunbroker for $200-250) and having a manual safety installed on that frame for use on the rifle. I also plan on having the muzzle dec turned off and the barrel threaded by a gunsmith. My MechTech: The original telescoping stock latch: The new telescoping stock latch (with retaining screw removed): That's all! Feel free to ask any questions you might have and I'll be glad to answer them.