I've never seen a load that required variation due to use of a silencer.
The loudest sound component is the muzzle blast, but when you're shooting out to distances of 100 yards+, you can definitely hear the sonic boom. It's pretty cool to first hear the muzzle report, and then later, as a distinct sound component, hear the sonic boom. It's not necessary to create subsonic rounds, but it makes the round much quieter.
If you're using a silencer to help reduce flinching, then the sonic boom won't be an issue. Using a silencer in BR shooting provides a distinct advantage, even more so for beginners or the lesser skilled shooters.
As to the barrel harmonics issue, I think that is a highly overrated aspect of shooting with a silencer. The silencer and barrel harmonics may work to reduce your group sizes, but it may just as likely enlarge your groups. I've seen both. Most likely, unless you have bad mounting or barrel alignment issues, it will do nothing other than probably shift your POI a little.
Did you get a 300 can or one sized specifically for 243/6mm? I haven't seen a silencer made for 243, although I haven't paid attention to that market.
