I picked up Standard Manufacturing's SKO semi-auto 12 ga. and love it so far. It is made in the US with there upper and lower (AR Style) both being milled from solid billet aluminum. Feeds reliably with everything from birdshot, slugs, and 00 Buck as long as the velocity is at least 1200 fps. The manual says after the break-in period you can shoot cheap low velocity Walmart Special ammo but I have not given that a try yet.
Standard makes 5 & 10 round box magazines and just came out with a 25 round drum. I got a half dozen 10 rounders and am using the SKO for local 3-gun matches. Since I use an AR in matches the transition to the shotgun is seamless having the same type of platform. I paid $46 each for the 10 round magazines from the manufacturer but you may be able to find them cheaper on Gunbroker. It takes common chokes (comes with one skeet choke - 5 thousandths constriction) and I purchased an Improved Cylinder choke for the longer range targets at our 3-gun matches.