I just got a .300 black out pistol and thinking about what I wanted to load for it. I see why a lot of folks like these things. I got a bunch of AP's but don't know if subsonic loading would be worth the effort. No intent of use other than seeing what a 10.5" barrel with 1:8 twist might do with AP's to some junk around the house. The AP's are 125gr. I think I'll need a pretty fast powder. Thoughts?