Right, here is the exact loading, taken from the Armourers bible, the EMER's
The weigh at unit workshop level must be between 3 and 10 pounds
At Field and Base workshop, it must be between 3 and 7 pounds
Sniper rifles must be between 3 and 7 pounds at all levels.
The barrel should bear evenly along the 2" or so raised portion and there must be a clearance of at least .020" along the sides of the barrel. Under no circumstances must the No4 barrel touch the handguard