This one I built from extra parts laying around the shop.
It is called a guild rod build from the rod going through the center of the gas system. Yes that means it is gas operated.
It shoots the 7.62x39 round, barrel length is 3 3/4" including chamber, it weights a little over 4# empty, it will take from a 5rd mag to a 75rd drum mag.
It is accurate out to about 20yds, but the muzzle flash will knock them down even farther. It is a lot of fun to shoot and gets a lot of attention at the range.