Well, having collected my 300S on Sunday, although I guessed that it would not be pellet fussy, a quick search revealed this old thread.

Thank you BBS.

I don't have any dedicated match pellets, but have plenty of Hobbies. Today was my first chance to try my newly acquired beaut out and I can confirm that it absolutely loves the Hobbies. So, nice and cheap and widely available. They'll certainly do for me for now, although I will try some others at a later point.