Thats a good question for someone like Roskoe. I would quess that opening up the mouth effects the shoulder as well and maybe adds a little more powder space. However although I have read the ballsitics, I don't remember them right now. Its not a high velocity cartridge though. I think it has a 210 grain bullet and a 180 grain bullet in its factory loads. The factory, using blends of powders that are not available to handloaders give the an edge to start with at least.