I knew of these saws for some time, but I never thought I would be able to get one in our collection. Basically it is the first form of what is now the 075-076 series saws. It is built on the 075 chassis with a two piece head and tuned muffler. This 050 AV was a factory In-house production before the 075 was put into full production. I am not sure if the two piece head was a trial casting of what is now the 075 cylinder, or made to make it easy to get to the transfers of the cylinder. (What I mean is in casting a cylinder head it is easier to do a 2 piece than a one piece. But if it was designed to be a true HIGH RPM type top end, then the two piece head would make it easier to modify the tranfers and such.) Cutting with it shows it's a high RPM cutting saw, but I also see how later followed models did not have that speed off the top end and were strong on the bottom end (torque). Stihl had a cart motor many years before this was made so I doubt this was in response to the Mcculloch kart engines loggers were putting into the Mac saws. Either way it is a nice saw to get a close up look at and super fun to run!