hole size

I have two shrouds, one with a 7.5 mm hole and one with 6.5 mm hole. Basicly you want the smallest possible hole that you can drill without letting the pellet clip the baffles, the better the alignment the smaller the hole that you can drill. My advice is start with 6.5 mm and see if the pellet clips the baffles. If it does then work your way up.