Maybe I didn't explain properly - the pellet is a gnat's pi55 too big and needs to be pushed in, quite forcefully, with a little plastic thing someone kindly gave me.
ok.. well in my hw97s the superdomes fit fine, as do ever pellet I have tried.
I haven't used a stoger x20s though so I cannot directly compare.
Daystate rangemaster Li are quite 'short' stubby little pellets, you could try those.
all the best mate, SKoT