Hello all. I have lurked on this site fore a long time and decided to finally sign up. I Am thinking about purchasind an Arsenal Sgl 20 from K-var and am wondering if anyone knows if the parts on this rifle are interchangable with other AKM parts. For example if I have a Wasr 10 could I use the gas piston or bolt from that rifle in the Arsenal one? Also I am at a loss as to the difference between the Sgl 20 and Sgl 21. As far as I can see the specs are the same for both rifles. Perhaps of overlooking something really minor. I have tried to find the answers to this on the web but not had much luck. Thanks!