Scythe crossing a pen, backed by a circuit

Attempted Sub-2000 Mag Carrier

Patrick Tait, HoA chief Mad Scientist
HoA Laboratory, Department of Ballistic Science, Dakka sustainment division.
Fully extended Sub-2000 with magazine attached to the buttstock

I've always loved the idea of takedown guns. Part of it was the simple joy of taking things apart combined with the complex joys of firearms, part of it was the James Bondian ideal of having a full rifle that could be carried around in a suitcase or even a violin case sounded nifty to 5-year-old Patrick. That's where the initial attraction to the folding Sub 2000 came about. It's not technically takedown, but it's ability to fold in half makes it almost as portable as a takedown, it fires a common caliber with common, easily available magazines and has a decent after market community.

After a lucky bonus check I finally decided to take the plunge. I purchased an early 2nd generation Glock model in 40 S&W. It's more expensive to shoot than the 9mm, but if Ballistics By The Inch is to be believed it shoots equal weight rounds at a higher velocity than a 357 out of a 6 inch barrel with a larger diameter bullet, so something I'd be confident to do some hunting with as well as plinking and home defense. It's fun to shoot out of box, but I never like to leave my tools unimproved.

I always had a specific vision for what I wanted to do with my Sub 2k. This included a shoulder rig, integrated red dot that allowed for folding, instrument case storage and on-rifle magazine storage. The fist three will have to wait for future projects. An attempt at the last one is the subject of this writeup.

There was a Kel-Tec produced magazine carrier that mounted to the inside of the stock made for the first generation Subs, which is where I drew the inspiration for this design. Sadly, even before they came out with the Gen II the magazine mount was almost impossible to find and seems to have been forgotten by the company. The website has no information on the mount, although Archive.org has a copy They haven't made it for the Gen II yet (and I would be somewhat surprised if they did). On the other hand, the Sub community has a fine, old tradition of modding the crap out of your rifle, so who am I to break tradition?

The basis of this modification is the Fab defense GMF G picatinny attachment base plate. It adds a female quick detach picatinny mount to the Glock magazine. Now, I don't have a Glock pistol or any other pistol with an underbarrel rail, but the mounting options for the Sub were obvious. The sub has rails on the forearm as well as a small rail on the bottom corner of the stock. Mounting on the front rail was not practical; you have to slide the magazine on and off, so if there's a light on the rail the mag has to be in front of it. Mounting it on the rail that's already on the stock means that you have several inches of magazines dangling below the gun, making it somewhat unwieldy. Adding a new rail seemed the best solution and the obvious place to add the rail was on the inside of the stock, just like the original Kel-Tec mag holder.

Glock magazine with Fab Defense baseplate installed

I picked up an M-Lok rail segment attach to the stock, both because they were reasonably cheap and because it gave me a chance to play around with the mounting platform. I had to modify both the stock and the M-Lok rail to fit with each other. The M-Lok rail has four lugs on the bottom to hold it in place in the corresponding slots. I could have carefully measured out the exact dimensions and file four notches on the stock, but I decided to be lazy and file off the two inner lugs on the rail. That way I just file a hole in the stock for one lug and mark the stock for the second. Since it's going to be epoxy bedded and not a precision mount like a scope I decided it shouldn't be much of a problem.

To permanently attach the rail segment to the stock I decided to use JB weld. JB weld alone won't be sufficient for this application, it provides good bedding, but with the strong recoil of the Sub I was willing to bet that it would shear off rather quickly. Since the M-Lok rail came with screws I decided to drill and tap the epoxy bed and the stock and use them to hold the rails more firmly in place.

Filing a slot in the Sub-2000 buttstock to fit the recoil lugs of the M-Lok mount Holding the modified M-Lok mount to the slots in the Sub-2000 buttstock

I used cut up loyalty cards to hold the epoxy in place, they were the perfect slick plastic that barely binds with superglue and JB Weld and can be pulled off with no issue once everything is set. It took about 15 seconds to drill both holes, 2 minutes to align the holes, and 10 minutes to get the drill press out and back into the closet. I need to move to a place where I have a dedicated lab space.

Sub-2000 buttstock with a picatinny rail being epoxied on it.  Dilute kitler in background.

I measured it with my eyeballs and not a level it and as a result it is ever so slightly off axis. The magazine being canted won't noticably effect the utility of this mod, but does show that precision work requires precision prep. When I use a similar technique to mount a rail to an aluminum block for a front sight replacement project, I'll add a few extra steps to make sure it's perfectly leveled.

The magazine mounted to the buttstock, noticably off center

The end result looked good enough, not like it was a factory made but not horribly out of place. The magazine is in an easily accessed spot that doesn't get in the way in normal handling and use. It adds a bit of weight to the back of the rifle but that's not noticeable when shouldered. Mag changes are pretty easy, realistically it's not going to be faster than a mag holster but for a home defense bump-in-the-night rifle having a mag holster isn't always practical. Overall I really liked the result, with the minor complaint that the recoil renders it completely useless.

On an average 15 round mag dump, I lose one round and the second is driven into a position that makes the gun fail to feed. I may end up making a cap out of shapelock but at that point the manual of arms gets complicated enough that I have to question the utility.

No regrets, not even on the parts purchases. Even a failed project taught me a bit about fabrication and help let me know what is and isn't practical for future projects.

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All works on this page is copyright 2009 Patrick Tait. Some rights reserved: creative commons attribution 3.0 license