I think the junk chance quoted in game is wrong.

I just disassembled 5,000 maple logs and so at a junk rate of 49% (I have junk chance reduction 2) I should have got approximately 5,0000.51=2550 simple/living components. However I got 2730. Now you could say I just got lucky but the chance of getting over 2700 is 3.1610^-7. Wolfram Alpha did the maths for me. It works out the chance you get that amount or less. So to get that more than that amount I took their value from 1.

So I think this quite strongly shows that the in game value of junk chance is wrong. If you want to help contribute to accurate junk chance values please disassemble a large number of an item and submit your results here.

EDIT: thanks u/NintendoToad, maple not magic logs