Originally Posted by
u.k.neil
Whenever a brand of pellets is changed (sometimes even different batches of the same pellet) or if the barrel has been cleaned then the barrel has to be "conditioned" to that particular pellet by putting at least ten shots (I do 20 to be on the safe side) through it before trying a group.
Different brands of pellets have different percentages of elements in them which affect hardness, coefficient of friction, B.C's etc which all have an effect.