I've got an XD9sc and I've invested in six 16rnd mags with extension sleeves. I want another XD that can use the same (16 rnd) mags. I know the obvious - an XD9 service or tactical, but are there others I might not be thinking about? I though I read somewhere I could take an XD40, and put a 9mm barrel in it and use the 9mm mags. Is this true? That might be a good option for me. I want to have a backup handgun in a SHTF scenario. What else?