I got some plywood at menards but it's has bunch of voids in the plys...I expected the bc grade to be a bit better.
BC grade is just what it sounds like. Grade B on the front face with voids filled and sanded. Grade C on the inner plies and the back face with void left as-is.
If you want good plywood you need to get cabinet grade plywood which is typically birch. If you can't find a cabinet grade then you need to atleast get a grade that is the same throughout (all plies are grade B).
I would not use MDF core for structural components. There are a lot lighter, better structural integrity products available.Maybe I should ask, how strong is mdf core plywood verses standard plywood? I'm wanting to make an entertainment cabinet under my 135" screen to hold my reciever, movies, speakers, etc. etc.