I just picked up a used SPR310S in 20 ga., and although it's a little on the heavy side (it weighs in at 7 lbs 4 oz on my scale) it appears to be a well made gun at a very reasonable price. They are made in Russia by Baikal.
The only complaint I have is that the selective ejectors are not always selective, and about 1 out of every 20 times, it ejects both the fired and unfired round together. I think this is because the ejector springs are so powerful - they throw the empties about 12-15 feet.
The screw in chokes use the Tru-Choke threads which most big places like Cabela's, D1ck's, and BPS don't carry, and a lot of the smaller shops don't have them either. However, you can get them from Carlson's (www.choketube.com
). I just bought Skeet and IC tubes for the SPR 310, and Carlson's included a storage case and choke tube wrench for free. I ordered on a Sunday, and they were in my mailbox on Thursday.