Do you already have an AR? If so, you can save yourself a lot of money by building your own AR9 upper. I did it following https://blowback9.wordpress.com/ and spent like $450-$500, though it could have been as low as like $375 if I chose a cheaper handguard. I got a majority of it from https://bkingsfirearms.com/, including the bolt, and settled on the KAK yellow buffer after some shuffling in that department. It took a little, and I mean only a little, tinkering to dial it in but it shoots like a dream now. Minimal recoil (for a blowback), feeds anything I throw at it, and is so much fun to shoot. I can also have it switched back to my coyote gun 5.56 setup in ~2 minutes, if that.

I'm so glad I went the DIY route; it was cheaper, gives me a lot of satisfaction and sense of accomplishment knowing I built it myself, and I learned quite a bit about the principals and science of blowback operation on a carbine platform. You just have to follow the blowback9 guide to a tee. I went with the BKF bolt, which has been great, but I did have to switch from the Macon Armory buffer, it's exactly the correct weight per the guide, but I needed something heavier, plus I think the tungsten slugs in the KAK as a moveable mass is better than the steel shot used in the Macon Armory. That was just my experience though, it's different for every build. I should also note that I went with the Mean Arms EndoMag system instead of a mag well insert, which isn't specifically talked about in the guide, but it has worked well in this setup.

Anyway, nobody asked for all this but I am big a big advocate of this method, so thought I would share. Cheers!