Being someone who has loved the Lumberjack since it's release (and making one of those imfamous Lumberfish) I will say it is a highly communicative weapon since the arming rate.
I have read someone mention a good loadout, however I tend to go for Lesmok, Charged, and Incendiary. Again, Lesmok for distance, Charged for medium, and Incindiary for up close; however, I also have charged for if they get too close for the Side mortars.
As a Pilot of a Lumberfish, half my job is to watch the damage indicators and relay the info to the Gunner, just in case they don't get it. I also give them great praise (the first time I flew my Lumberfish in Ages, I had a Gunner who got us 5 kills in a 3 v 3 deathmatch...granted 3 of those were side mortars...) it's a tough gun to use, but I think it's the most fun, definitely when you can utilize it well.
Basically, as a Pilot, you have to know when to go from long, to close, to "dang they're too close" combat, and keep in touch with your Crew, let alone contact with your other captains.
As a gunner, you just have to get a feel for the rounds and the arming. Again, I chose incendiary for closer range, but the drawback to that is that incendiary rounds drop immensely, so you have to aim higher.