I have a mag block adapter if you want-- just take out your bolt catch and slide it in from the top. It's made for Colt mags. I have a dedicated lower, so I don't need it anymore. PM me and I'll send you the price, all you'll need is an upper and PSA sells those for pretty cheap with the bolt included. As for the incident from a week back, I spoke to both parties. It sounds like there was a bore obstruction; bullets stops, bolt starts going rearward until the casing clears the chamber and is no longer supported, and the gas vents out the path of least resistance. It sounded like a freak occurrence, and while you could argue that a different system may or may not have had the same results, I wouldn't let it scare me off of owning one. I'm surprised that none of the .45 fanboys made any comments about that being the one time a 9mm did some damage... Anyways, back to the build, I bought an upper from PSA. Came with MagPul furniture. Nothing fancy, I shoot her with the irons and she prints two or three inches at fifty yards easily. I use it for practice when I want to save 5.56, the 9mm holes are easier for my eyes to see on paper, and newer shooters like it because the recoil and muzzle report aren't as sharp as 5.56 is (which is already light). I've gotten mags from 44mag.com and they'll range from $15-$30 depending on availability. Much cheaper than Sig MPX mags! I'm currently working on one that'll feed from Glock mags, that'll make pistol/carbine matches much easier to pack for. If you want to make this AR9 on the cheap, stick with the Colt mag setup. The lowers are cheaper, and the last round bolt hold open is much more reliable.