There are not very man choices for Barrels when it comes to 6mmx45 so I am going to go with BlackHoleWeaponry.com for my barrel. Now I have a choice of a Target crown or a 1/2-28 threading like an AR. I don't really care about the thread but I am planning in future to get a 308 suppressor that I would be able to use on the the 6mm and .223 if I do my HW and make sure I can get an adapter that will work that is why I am tempted to get it threaded. All of that said I looked down barrel of one of my AR's that wears a standard A2 Flash hider and it looks like the opening is quite large and I would guess has a good 1/8th of an inch on all sides around barrel. So what are your opinions about running an A2 birdcage on a 6mmx45?