Things to look for

1) Proper bow tune.Field points are very forgiving of improper tune, broadheads are not, especially big heads like a Magnus.

2) Arrow spine. You may be underspined w/ 125 grain points

3) Make sure you arrows spin straight and the inserts/broadheads spin straight as well

4) Ensure you have enough fletching control. Magnus are a big head requiring big fletching/helical to get good control. Minimum of 4" helical vanes/feathers. 5" would be better.