How to make a circle tween animation

Hi everyone

I'm trying to make an animation and it seems like an impossible task. I'm not a beginner, and this is harder than it first seems to be.

So this is what I need: to make a tween between a partial small circle to a big circle. What I mean is I want to use the Oval Primitive tool and on frame 1 I'll have a circle (radius 100px) with Start Angle: 0 and End Angle: 230 and on frame 50 I'll need the same 100px circle with Start Angle: 0 and End Angle: 300.

I tried using Shape Tween between the two frames (with both Blending modes, Angular and Distributive), but nothing works properly. HELP! What can I do?

If you could post a link to your file, I'll take a look at it. I need to see what you're talking about a bit more clearly and viewing the file would make it a lot easier.