(SIDE TOPIC MADE INTO NEW THREAD - MODERATOR)
It is a standard 12 round USPc/p2000 mag with a spacer sleeve on it. I was looking at buying an x grip spacer, but at $15 apiece and having near 20 mags, that is getting expensive. My son does 3D printing, so he down loaded a sleeve for a p30 mag, and the. Started to modify it to fit the P2000 to SK set up.
This is a picture of the prototype he made after modification. It still had some gaps, so I took this pic so he knew what to modify. Once we got the dimensions down, I had him add the HK logo on one side an P2000sk on the other so I would know what they went to if for some reason I took them off the mags. It takes a couple of hours to print one, but he has multiple 3D printers now, and uses them to make extra money during the pandemic. Apparently, he gets all kinds of strange request to make custom items... like the guy who wanted a section of the Death Star molded and printed to fin in his aquarium. He emailed me because someone wanted him to make a Glock frame... had to give him the big NO phone call before he stepped into an ATF bear trap.
Here it is with the 12 round mag and 3D print sleeve, and the standard 9 round mag in the gun. If I were to carry it ankle, the 9 round works well, but AIWB, the 12 really does not add enough bulk to worry about.