I've never shot Black Mag3 but would sure like to. How it will work with the big conicals will have to be seen. If you have any Triple Se7en around the house, take some with you. You might want to see how the conicals shoot with about 80 grains of that.
I've shot Mark's bullets. His 300 grain Spitzer did real good out of the Black Diamond XR but I am (as you can tell from the photo) a real fan of Buffalo Bullets. My favorite are the 375 grain Buffalo Bullet SSB's. I load them with 100 grains of Goex 3f and the accuracy is outstanding with them.
I know all about taking the finger off with the front sight on the rifle. I have done that myself a couple times. Kind of hurts when your standing there with blood pouring off your trigger finger...