Something to be mindful of when using subsonic ammo is to know what kind of velocity and stability you're getting with the ammo you're using in your specific barrel. Long and heavy bullets are tricky to stabilize so you need to be sure that it's getting done or you'll get baffle strikes which are nasty. What may be just barely subsonic and perfectly stable in a 16" barrel might not be fast enough to be stable in a 10.5" or 8.5" barrel. The Blackout is designed to not lose nearly as much velocity and energy percentage wise as 5.56 does, but it does in fact still lose some.