There are lots of variables but with the Brinnel hardness number you listed (16-17), assuming everything else is right, maybe 1200-1300 fps.
Elmer Keith's alloy was not as hard as you mention so maybe even full velocity. With commercially cast bullets frequently the lubrication is lacking, meaning the quality of adhering to the bullet during shipping is more important to the maker than proper lubrication while shooting. You also see bevel bases more now which probably works against optimum sealing, but makes loading easier.