Gaddis, the Mec Jr resizes on the first stage to (so to answer your question Firedawg, yes the Mec Jr resizes).
I think the differences are that the Sizemaster comes with the auto priming feature and has a collet style resizer. Where as the Mec Jr uses a sizing ring and the auto primer is an upgrade. I have a Mec Jr (pre Mark 5 model) that I parted together from two different machines purchased at a gun show (about $25 total), works great. I added the auto prime assembly to speed things up.
There may be other differences to.
