Glad to be of help. But I honestly don't know how effective Testor's Dullcoat would be as a wood filler. My guess is that if it's thick enough to fill the pores, and it sticks, and it dries hard, it will work. That's assuming, of course, that you intend to paint over it. I don't think I'd recommend it as a clear wood finish.
The key to a good finish is a smooth surface. Furniture makers often talk about the problem of "raised grain." That's the phenomenon that takes place when certain woods get wet; the grain opens up and the surface, when it dries, gets rough. With birch dowels that shouldn't be much of a problem, but if it is there's a solution: raise the grain on purpose. Wipe the wood with a water-dampened rag, let it dry thoroughly, and sand it smooth. Then apply whatever you're using as a primer.
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