basically all marker breech can fit all pellet sizes , it's just that the Barrel's bore that might not be able to fit all the sizes.
Pellet comes in few sizes, 0.688 , 0.689, 0.692 , so does the barrel bore.
hence if you're using a barrel with 0.692 bore size, you practically can shoot every type of pellets. However, when the ball-to-bore size doesn't match, pellets tend not to travel in the straight line when it leaves the barrel due to the uneven movement while travelling in the bore.
using a barrel with 0.688 means you can only use pellets that fits it. if not, ball break will occur in the barrel and you'll have great time cleaning the barrel during the game.
usually in a barrel, pellets gain speed in the first 8inch of the barrel. the remaining few inches are there to guide the pellets to the direction that it's suppose to go ( pellets tend to float in the barrel after the first 8 inch. )
hope this answered your question.
does it means in tournament player usually use barrel bore which is matching the pellets supplied ?