Now this is not fact but how I understand it. Lead will seal the chamber better than jacketed bullets. Swaged will seal better than cast. I am fairly new at reloading but I would have to look at the pressure of each round. 5 grains of "whatever" will have different pressures on each of the three...
To reduce the risk of chain firing. (Something that can happen alot) After the powder I fill the cylinder full of regular old corn meal. Like you make corn bread with. It helps prevent chain fires and also gives you a consistent compression of the powder.