I wasn't aware of the 'standard' as being .512, as .50 cal barels I see listed by makers here, are .510". I'm assuming the .512" is normal with double rifles or the Express rounds. I am unused to using bullets not exactly bore size.
: I do agree with 4831 being immensley cooler than cordite, but compared to most powders I use today, it 'is' hotter burning - but perhaps only when used in it's desired pressure ranges in the small bore magnum ctgs. like the .300's. In those, the ball powders are much cooler burning but due to their not being generally usable in straight cases, they aren't used in the express rounds. My straight cased .458 2" shot extremely well with H335 powder & 510 gr. Solids at 2,050fps, matching my best results with stick powders. I don't know of one suitable for the 3" .500 Nitro, though.
; I've had good results with large bore straight cases and card wads, but,as I stated, they must be under the bullet.