Let me try again ?
4 identical bullets out of a CNC machine. 1 ea.cup and core,bronze,copper,wheel weight. All fired at the same fps in 1 gun all should have the same target performance ,same group similar impact point. In point if they are wad cutters or the like they should all clump together. Pointy bullets don't/won't do that. The bronze hit hi ,copper goes pretty much where it feels like,cup and cores generally go where pointed,and lead often tumble & pattern. Why? It can't be CG as all of these are of the same shape and dispersion of weight even though the weight is differant its in the same place. Bbl friction is only differing on the lead and copper bullet but should be negated buy keeping the same fps.
That's not exactly identical is it? If they are the same weight they aren't going to be the same length. If they are the same length they aren't going to be the same weight. Since they are all made of different material they aren't all the same density. Since they all use different jackets, or none at all, they don't have the same friction traveling through the barrel. Since they all create different ammounts of friction they require different pressures to reach "X" velocity. The list goes on and on and on.