I've started the process, shown
here.
The ammo I'm going to use for vetting is stuff I've had for a while that I want to get rid of - 75 rounds of Federal birdshot, 30 rounds of Estate low-recoil 00, 40 rounds of Winchester Ranger low-recoil 00, and a few boxes of Federal Truball full-power slugs which I have no idea why I bought. I plan to zero the gun at 50 yards with low-recoil Truball (actually, this will be step 1) and then pattern eight- and nine-pellet Federal Flite Control 00 to see which it prefers. It will end up loaded (full magazine and sidesaddle, empty chamber) with its preferred buckshot. It's going to be an inside-the-house gun so I see no need for slugs, especially with the FC ammo. I'll keep some slugs on hand anyway, because reasons.
I had already signed up for a shotgun class next month with Steve Moses, so I've got that covered. Shotgun training is harder to find than carbine training, at least around here.
Thanks for the feedback!