You need to maintain the heatcore before each full day of play.
All you want to do is remove the heatcore and apply a very light coating of high grade marker grease to it.. If your bolt guide comes out, make sure you re-insert it with the tapered end in the barrel and the square seat edge to the heatcore spring.. No oil is required.
The mk3 k series is pressed aluminum while the M series is milled aluminum. And the square head like shocker monkey said.
Paradigm pro shoots FS rounds as well as .68 paintballs
K series shoots only .68 paintballs