Reloading .303 British : 120gr 32-20 hard cast lead for downloading

Many years ago, a friend of my Dads shot light weight cast lead bullets through his No. 4 in his basement. I still have some of those bullets and believe they were 120 gr .32 calibre. 

I don’t see any reason why that would not work. Typically a pistol powder like Unique. Has to be a fast powder to get reliable ignition. When I get back home, I’ll look to see if I have load data for that bullet in the .303. 

Is there a muzzle velocity maximum you need to meet?