Because of his experience.....
....which exceeds mine by about ten miles, I am reluctant to even mention these things, but then not knowing what I am talking about never impeded me from speaking.
I wonder about the sizing of the bullets coupled with the way in which the bullets were dropped.
I don't know where that rifle slugs out. But with microgroove rifling, the size of the bullet in comparison with the actual bore dimensions might be critical.
Also....(And this is also because I am ignorant) is it possible that softer bullets might be better in that rifle?
Your friend obviously knows more about it than I do, so he will be able to quickly eliminate these factors from consideration.
My reading of history convinces me that most bad government results from too much government. Thomas Jefferson