The small capacity of the 300BLK is ideal for subsonic loads that is in fact one of the primary reasons it was developed. The loads that Rumbler list for the 208 grain subsonic load fills the case about half full and doesn't create a problem . The danger as he stated is that if you start at to low of a charge there is a danger of having a bullet get stuck in the barrel that is why you start a little high and work your way down to subsonic .