I've got both short chambers and long chamber 16 ga. I was hoping the press would accomodate both, but seems like it won't.
One of the members at the 16 gauge site stacks a penny and a quarter (I think that's right, but there is a thread on loading the DR16 wad that has the photo) underneath the round in the 600 Jr. when he loads shorts or you can buy the plate for $20 +/-. The easiest course is to load shorts and shoot them out of both guns. You won't suffer ballistically if you are content with 1 oz. and less. You can buy primed cheddites precut to 2.5" or DIY out of 2 3/4. The bigger issue is re-sizing the brass. If it is truly brass and not brass washed steel, the Jr. can be fitted with a re-sizing ring that is relatively cheap. But if you are going to re-size steel, you'll need the collet re-sizer.