I appreciate all the advice. To update my progress, I did receive my shotgun, quite a heavy beast. Someone on another forum posted a 1908 Sears advertisement that priced my gun at $35.25, a $10 premium for Damascus over "armor steel". Between Buffalo Arms and Track of the Wolf, I rounded up 20 turned brass "Parker Bros." cases, wads, etc. E-bay yielded an antique loading kit, in the box even! I learned the original standard load was modest: 1 1/4 oz shot over 3 1/2 dram. The loading kit includes an adjustable dipper with gradations for powder on one side, shot on the other. I found that the 3 1/2 dram powder setting loads 1.2 oz #6 shot and 2 3/4 dram by weight of Alliant Black MZ. Seems conservative, so I put together 4 rounds and to her to the range. Given 10 gauge with full and extra full chokes, I set my cardboard at 40 yards. Recoil was mild (heavy gun, light load) but that target was evenly peppered. Could be a vintage turkey killer. I had my chrono along for other work, but I didn't check my shotshells. Next time. One thing missing from my load kit was a decapper, so I made one today with a 3/4" dowel and a pin from a Hornady universal decapper. Works fine.
Today, of course, a 10 gauge is a real fire-breather. In 1907, not so much, but still an effective relatively long range piece. Come fall, maybe she'll kill a turkey.