Rob,
I would suggest you start with something like RWS Hobby (7.1 gr.) or RWS Meisterkugeln Pistol (6.97 gr.).
I generally use RWS R10 Pistol (6.99 gr.) in my HW30S for the MPL.
I have not found the HW30S to be 'pellet fussy'.
Have fun
Best regards
Russ