I am in the process of acquiring a Remington 5r in 308. I really want to use it as a basis for a compact 308. The gun will almost always be shot suppressed. My question is how short can I go and it still be effective. I plan on using it for no more than 600 yards. I was thinking about cutting the barrel down to either 16 or 18 inches.. Any input or experience would greatly appreciated.. thanks