True, there are lots of variables. When a round is traveling at about 2,000 fps and contacts flesh a phenomenon occurs called hydrostatic shock. Essentially the flesh expands so fast that elasticity is overcome and the flesh shreds instead of flexes and returns to shape to some degree. There are basically no handguns, of that time anyway, that send a round that exceeds that 2,000fps threshold. Rifles, with "necked" cartridges and more powder regularly achieve the 2,000fps threshold. Though the round that Oswald allegedly used was a 6.5x52 carcano and at that distance it would have been right at that threshold whereas a round from a pistol, even just feet away, would bit have caused hydrostatic shock. For sure there are lots of variables like you said.