If you use flat heads (Bisley Practice work well) then you avoid strain & jams in loading mech as it doesn't need to push the magazine follower and pellets back to index the next pellet into battery.
That's why I've always used RWS Hobby's in mine, as advised to do so by the seller of my first 600 many years ago.
I've only got one left now having recently sold both the boxed ones.