As a drilling nut and general combo gun sucker I have to admire the drilling.
I've had, shot, and loaded for drillings for 60 years. I got my first one, a Charles Daly 12ga/30-30, at age 12.
Please follow this advice. NEVER load for velocity! Always load 'softly" for these guns. They were made as light as possible, given they have three barrels. Consequently, they were built marginally strong and don't like taking beatings from hot loads.
Two Things:
1. It's a 65mm chambered shotgun, so get some RST 2 1/2" shells with no more than 1,200 fps velocities.
https://rstshells.americommerce.com/sto ... Gauge.aspx2. The rifle is REGULATED for One specific load. It will be the most used factory load for its time. Find out what the bullet weight was, and find out the muzzle velocity, then load for that mark. It's what will make it shoot to the open sights and to where the scope was sighted in.
These are a bit like regulating double rifles, something I've done a bit. As you increase velocity they shoot lower. If you shoot lighter bullets they shoot lower. If you shoot heavier slower bullets they will print higher. As the rifle barrel warms up they will shoot higher and probably to one side or the other, so sight in with a cool barrel. Usually take two shots and cool it down well, then repeat.

It's great to see her being used again, and I especially like the photos. Please post more as you hunt with the gun.