Basically, the 6.5mm round is caseless, in all weapons. It comes in 30rd straight Stick magazines (being a little wider than your 5.56 STANAG but shorter and straight), 100 Round Sticks, and 200 Round Boxes, which the Mk200 would have. All caseless.

That said though, the CSAT Katiba uses 6.5mm Caseless rounds, but of a different magazine. Think of that round that CSAT uses like the different between the 5.45 Russian and the 5.56 STANAG today. 

Replying to your queries- everyone else, see if you can get to work getting CSes up- anyone is clear to post up.