Big and slow has something going for it.
My 45/70 Handi single shot uses a 405 gr. soft home cast that's hand loaded with a small dose of Unique this time of year.
Old chrono reads just under 1000 fps. Very soft shooting, and has been effective for me out to at least 100yds. or so.
If interested in "Low Velocity Lead Bullet Chronograph Data" may want to check this out. Load data. An oldie but a good one: