Here's the background on the idea. Since it's the summer I've been carrying my Kahr PM9 quite a bit in my AIWB holster I made for it. It's a perfect carry gun if you can live with it's shortcomings such as shooting comfort, short sight radius, caliber & capacity. I've overcome comfort issues by adding a Pearce finger rest to my carry mag and by practice I can overcome the sight radius. I'm actually a fan of 9mm because of it's availability/price and with quality ammo it's a proven killer so caliber's not an issue for me. I have always been a tiny bit bothered by it's 6+1 capacity and I've been preached to before about always carrying an extra mag. I've always wanted to be able to carry one, but I've run out of pockets to drop one in and I have never been too thrilled at the meager offerings for IWB tuckable mag carriers. Yes, being tuckable is always a requirement for me. I'll get into that in a different post.
Then I had a light bulb moment. The issues I have with vertical mag carriers is that in order for them to be concealable with a cover garment they need to be positioned high on the belt. This can cause the top of the mag to poke you in the ribs. That's with OWB carriers. With IWB carriers they take up valuable space between your body and your belt. Almost all of the spare mag holders I've ever seen have been vertical except for a few, one by Galco and one by Safariland, neither of which are tuckable though I do like the simple concealable design of Safariland's except it uses noisy velcro to get to the mag. There are some simple kydex or kydex/leather designs out there that are tuckable, but all those place the mag vertical so that it adds bulk between you and your belt. My thoughts were that if you could place the magazine horizontal above and in line with the belt it wouldn't add any bulk to further squeeze my tender waist. My choice to make it out of super thin kydex came because I actually had a couple of sheets of it already that I'd been playing with. This design could be adapted using leather, but that involves skills I admit not having. The retention of the mag is through friction by tightly fitting the kydex around it. It won't fall out when turned upside down, but will pull free when grasped and pulled.
Next I had to decide how to attach it to my belt so that it wouldn't move or pullout unless I wanted it to. In this design the magazine is basically sitting on top of your belt so there's no real chance it'll fall down your pants (unless you wear your pants very very loose) so the attachment point would only be to maintain the carrier's position and to keep it from pulling out if vigorously accessed. In this instance I choose to use velcro because my Crossbreed gun belt is lined with it already and it's as stealthy as you can get. In the pictures you can see the generous gap I gave it to allow a shirt to tuck in. This can be made with less or more length based on whether you typically have a lot of shirt to tuck or shorter for more comfort when sitting.
Here are some pictures of it along with pics of it being worn.
Because tuckability is just an option it can be worn untucked for the few times I roam casual.
After trying it out for a day I'm happy to report that it works as expected. At this point I've just been wearing it 11:00 o'clock (opposite side from where I wear my PM9), but it could easily fit behind my left hip. It hides easily. I notice it's there, but it's definitely not uncomfortable. By untucking my shirt to access my gun I at the same time provide access to my extra mag if it's needed. Using an 8 round spare mag I can now carry a total of 15 rounds on me which is comforting.