Heavier, Slower Ammunition

First let me say I know the fishbones are coming because this is yet another invention in an unpopular field: weaponry

Before I throw my idea out there let me first start with a few facts about firearms the readers may or may not be aware of:

1)Adding a silencer or suppressor will can reduce the noise made by a firearm but can do nothing to silence the miniature sonic boom that causes an audible "crack" that makes the suppressor pointless unless one is using subsonic ammunition
2)Prime candidates for suppressors are usually pistols or submachineguns(which happen to use pistol ammunition) because little stopping power is lost by slowing down a pistol round to a subsonic speed
3)Rifles (both assault rifles and sniper rifles) depend on a small round going very fast (well above sonic speeds)
4)Once rifle rounds are slowed down to subsonic they lose much of their beneficial characteristics: Superior range, penetration and accuracy

That being said, this idea involves modelling a new round after (what I think) is the ideal ammunition for silencing, the .45 calibre pistol round. It is known for it's superior stopping power and "nail-driving" accuracy compared to other pistols. Another terrific characteristic is that it is naturally subsonic so no reduction in velocity is needed.

Now the jist of the idea is to make a scaled up version of this round along with a rifle specifically made for it, that has an integrated silencer similar to the MP5SD. This weapon would (hopefully) offer a marksman a long range weapon with devasting energy transference without the worries of alerting the opposition.