charlie brown

A reason that you may be getting poor penetration is because of the velocity of the bullet. There is so much of a change from so much speed to flesh that the bullet has an immense amount of drag put on it and looses more weight than the same bullet shot at slower velocites where the bullet may not lose so much weight because of less of a change and penetrate better. At those speeds, any soft point bullet could have the potential to break up. Best bet would be to go to a Barnes X, or Failsafe, or Trophy Bonded Bear Claw, that have all copper fronts and won't lose as much weight at those velocities.

I try to think of it like insurance crash test for cars.
Two exact cars are tested running into a brick wall at different speeds.
One is at, say, 25 MPH. The damage may be minimal and very few pieces will be left on the ground, and the front of the car won't "expand" to much and will retain most of its original weight.
The second one is at, say, 75 MPH. The car will be crushed to an unrecognizable clump of junk. Pieces will be scattered everywhere, and the car will have "expanded" more than the first, and weigh considerable less.

The bullets go through this same thing.
For example
A 7-08 and a 7 RUM. 140 gr. Sierra Kings at "standard" velocities for each. Both shot into same material at same distance. The bullet from the 7-08 will retain more weight and penetrate deeper because there is less bullet loss from the immense speed.

Does this make sense? I think the only way you are going to get better penetration is to go to a copper fronted bullet or slow down the speeds a bit with a heavier bullet.