Duffy has a very good position on this issue and I appreciate his response. I also feel you need to look at the 'real' shape of the bullet - most jacketed 'flatnose' bullets do not really have a flat nose with a 'sharp' edge to it like the cast swc bullet, they are ogived or rounded and their ability to leave an incapacitating wound channel by cutting a 'square hole' and giving necessary penetration is not as good as the same weight bullet in cast swc type configuration.
I would say this is more the case in a revolver than a semi-auto where wadcutter shape bullets or other sharp edged flat nosed bullets really give the revolver a more effective bullet shape to use. If semi-autos could feed square nose bullets as reliably as round noses, it would add a real boost to the capability of a semi-auto for field use.
About the easiest way to show the difference of the type of entry characteristics the bullet provides is to shoot both on a paper target - you will notice the 'flat nose' fmj does not cut a 'square hole' or one with a sharp edge - it cuts the same type of 'pushed through' hole that all fmjs cut with edges that close up after passage reducing the diameter of the entry hole. Swc or wadcutter types cut 'square holes' or those that have sharp edges and those are more incapacitating. And that's my two cents worth, lol. HTH. Mikey.