I have a 4" 357sig XD w/ a 9mm EFK conversion barrel. I have several SA 10rd mags that came with the gun when I bought it(during the ban), and have since bought a 12rd 357sig SA mag. I have been looking into getting some higher capacity mags(made more urgent by the current political situation), but am still trying to educate myself on my options, and have not been able to find much info. Here's what I have learned so far: Mec-Gar makes the highest quality aftermarket XD mags; and while I do plan on getting some, they only hold 1 or 2 more rounds than the full-capacity SA mags and I would like to get some higher capacity mags. I have seen the 32rd 9mm & 20rd 40s&w Promags, but the general consensus seems to be that Promags suck. I have also seen the similar looking 30rd 9mm & 20rd 40s&w National mags, but have not been able to find any substantial info or reviews on them. From the little bit of info I have found, it sounds like they are not the highest quality, and have issues similar to the Promags. I have heard rumors that they are a bit better than Promags, but have not been able to find anyone here who has actually used or owned a National XD mag, much less compared them to Promags. Surely some of you have experience or knowledge about these mags? Somebody... anybody, please?! I am also a little confused about a common feature of the National & Promags. Apparently they are both single-stack. Why is that? It seems to me that if you're going to make a high-capacity mag like a 30+ round 9mm mag(or 20rd 40sw), it would make more sense to keep them more reasonably sized with the double-stack. There's probably some fundamental reason for doing this that I don't understand, anyone care to explain? I know I probably sound like a clueless newb('cause I kinda am), but I would really appreciate it if some of you more knowledgeable and experienced XD talkers could help me understand this issue and find the best high-capacity solution.