It depends on the caliber. My -06AI I just fire -06 loads. They are accurate and good for anything I want to shoot. For wildcat rounds I load up moderate loads of Unique with cast bullets just touching the lands.
For my 7TCU brass, 8.0 grains of Unique and the RCBS 145 silhouette bullet is actually shot in competition in one gun. The fireformed brass is then used for my other guns. Nothing wasted using this method.
Lots of tricks out there. I have done the COW and CM tricks with low doses of bullseye or other powders. Took a 5 gallon bucket, stuffed it with insulation, cut a hole in the bottom and put a piece of PVC pipe part way down. Barrel part way down the PVC and touched it off. Biggest silencer you ever saw, but you do need to put some weight on the bucket to keep it from coming off the ground. Also going to get some dirt flying up if you have very many rounds to shoot. Did 50 rounds of 7sm in one sitting and was making less noise than shaking a rug.
Buddy of mine got an old stainless steel sink, filled it with spray foam, and shot thru the drain hole into a hole bored through the foam. Works good until the foam starts to fly. Ended up putting in the piece of PVC to keep muzzle blast from tearing up the foam. Still made a good silencer for shooting fireform loads in the back yard.
Be carefull no matter what you do. DO NOT put any type of heavy material into a bottle neck case without working up to your load. Restrictions within the case can increase pressures dramatically.
Steve