All you can do is seat the breach plug the same way every time and have the rod in the gun you will be hunting with and shoot it a few different times and see if it maintains consistency.

The other problem could be the rifle primers. I personally would never use them with any powder. The standard rifle primers are just not hot enough for me. I would suggest using the magnums but I still would not use them myself. I want as much heat/fire directed to the powder as I can. And with the more flame I firmly believe you will have a more consistent ignition in all applications. Especially in hunting conditions including rain, snow and cold temps.