I work on many kinds of two cycle engines and whether a chainsaw or a snowmobile they basically have the same type of bearings and inner workings. Obviously at the time when they recommended engine oil for a two-cycle mix it was because it was what was available. Then you got to the point we had two cycle oil, but it was still not good enough to run at light ratios. Fast forward to today and we have oils that can run 100:1 and do fine at it. There is no reason this won't work in the engine. However the big thing that will get you into trouble here is the carburetor jetting. You can mix gas at 20:1 or 50:1 and melt down an engine just as quick either way if the jetting is not correct. The fuel mixture is was keeps your engine and combustion temperature in check. Since the pre-mix is flowing through a jet together (but burns separately) 20:1 will flow less gas through the jet than 50:1 since the extra oil displaced gasoline. Remember the oil is only there for lubrication, not cooling!
All that said you can run a modern mix in the saw, however you need to verify your carburetor adjustments. Really if you own a saw you should learn how to tune it anyways so you can adjust for temperature, etc. In your case if you have a saw that says 20:1 and you put 50:1 in, it will run rich.
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