Congratulations on the beautiful Dougall Lockfast! For reloading, using nickel-plated brass with black powder is uncommon but can work. Definitely skip the ultrasonic cleaner, which can damage vintage brass. For cleaning, warm soapy water is best.
Finding a specific load recipe for such an old gun is challenging. Start by researching common black powder loads for similar shotguns from the era. Focus on using appropriate wads to protect the brass from the black powder's corrosive nature. Remember to always reduce the starting load data and work your way up cautiously when developing your own loads.
