I'm loading for a friend that would prefer that his brass is fireformed without bullets. How much powder is needed for a decent fireform with a belted magnum case?

I use anywhere from 13g for the smaller cases and up to 18g of Unique for the larger belted cases.

Start out with 2-3g less (about 15g,) in the larger cases, fire one and check, and adjust the charge depending on the burn rate of your pistol powder. Don't look for real sharp edges as the case won't get sharp until after firing with a bullet. If using Bullseye use about 1 or 2g less than the above numbers. Whatever you do don't fireform in a braked gun, it can split the brake. Don't ask how I know!

As a general rule I use Unique. To get the starting charge. Fill the case to the brim with Unique and weight the powder that the case contained. The starting charge is 10% of that amount.

Like Bob indicated rounded edges as normal and ok. Dont try to get sharp corners.

Thanks!