I hate to burst your bubble, but your bow isn't tuned, at least not tunedto arrows with 125 gn Phantoms. When you change anything about your setup, especially something as critical as broadhead weight,it always requires the bow to be retuned.

That's one of the very best reasons to learn to tune your bow yourself. It gives you a lot more freedom to play around and experiment with different arrow/broadhead combinations without having to be constantlyrunning back and forth to a shop.

Another thing is that it couldbe that you are right on the raw edge of arrow spine for those 400's with 115 gn heads. Underspined arrows won't hardly ever shoot to the same place twice in a row.It's very possible that you need to change to a stiffer arrow for 125 gn heads. If you did your own tuning, you could back off the bow's draw weight by 5 pounds and test whether arrow spine is the issue.