for very light loads, I havent found many medium size cases that 4.0 grs of Red Dot didn't work well. 5.0 would probably be safer to start..to make sure you dont stick one in the bore. Clean and lube the bore first. Also...soft cast bullets are excellent idea for these type of experiments. If you DO stick one in the bore, it isn't so hard to tap out with a cleaning rod. Hard Cast and/or jacketed bullets are a nightmare if you get one stuck.