Barnes, I use the same barrel you do, Pro Hunter. Bought it like a couple of years before the S&W takeover. Never gotten it to shoot any boat tail worth diddly. It shoots the lights out of most any flat base though. The absolute best boat tail I actually got it to shoot was a 6 inch 5 shot group at 150 and that was with the Barnes .451 290 grain. It's partner, the flat based .451 290 grain shot a 5 shot group ( my cold clean barrel test if you remember) at around an inch and a half at 150. I have no clue why she no like boat tails but I have never owned a ML'er that did. Glad yours likes them.

Edit to add: I've never owned a .45cal ML'er either. Maybe they have a tendency to shoot them better. I have no knowledge base with them since I haven't owned one.