I hate it when that happens.

Vertical spread is the one thing that a person can't fix himself.

Like Nigel said you must get a hold of a Chronograph to determine the velocity of each barrel. They need to be within about 15 to 20fps of each other.

If they are the same then it is probably a regulation issue. Is this a fixed regulation or can you adjust it yourself. (Don't try and heat the sodder yourself. That is a recipe for disaster)