I’m gonna try the axis arrows as my new hunting arrows. I’m wanting to try the hit brass inserts (either 50 r 75 grains) to make up for the wieght diff between the two arrows. I like a hard hitting arrow, just don’t like the bending of the FMJ’s. I shoot a Mathews z7 at 68lbs with a 27" 400 spine FMJ arrow and a 100grain swacker. What spine would I need in the axis when adding a 50 r 75 grain insert?