This is going to be so obvious that I'm almost embarassed to mention it. But, hey, sometimes the obvious gets overlooked, so somebody's gotta do it.

Volume is one of the reasons that acoustic mandolins have eight strings instead of just four. To get maximum volume, both strings in a course need to be vibrating at as close as possible to the same amplitude. A pick stroke that delivers a healthy punch to one string but doesn't touch or just barely brushes the second string is going to sacrifice volume. In practicing, a conscious effort should be made to strike both strings with the pick. When playing rhythm chops, dig in just a bit deeper. When playing leads pluck all the way through the whole course. It's sorta like classical guitar technique where your finger plays all the way through a note and comes to rest on the next string. If you just bump the string and go on to the next note you lose a lot of volume. It's like golf or tennis. You have to follow through.

Bruce