I like the commercially loaded Sub-X in an 8 1/2” barrel. I bought a couple boxes of the bullets to try as well. That’s the best use for a watermelon in my opinion - I’m not a fan of eating them. 🙂
A lot of the reviews I have read said most people didn’t like pushing them out past 50yds subsonic. You can safely push them faster but it will turn in to more of a varmint round because they will break up. I need to shoot some in water and check the expansion and if they stay together.