I have a question about sub sonic rounds.. I have never done much reading on this so excuse my ignorance. What is the purpose of these low velocity rounds like the 300 whisper, 300 blk out? I realize its low velocity to achieve sub sonic speed BUT why not load a 308 down with a super heavy bullet? My only possible theory is you are loading those cartridges designed for low velocity at full pressure and its probably more efficient and consistent that way? someone help me out.