Mauser first off the BT isn't want I call a great choice for the likes of black bear. Yes their will be those who say I shot them with one before or my grand dad killed bears with a 22LR, etc...but bears have extremely large shoulder blades, thick muscle and hides. What you want to drop a bear is full penetration and the ability to get through that shoulder blade. Most inexperienced guys aim to far back on a bear for the perfect H/L shot, often leaving a one lung hit/liver...just like deer one these hits can go either way! Or they will over compensate and hit flush shoulder, this is a good shot on a yogi but you must have a bullet that will get through. Being you want a deer round at the same time, I would look into a Nolser Partition, Nosler Accubond or Interbond by hornady. These bullets will work both animals nicely and give you assurance that if you make contact with that solid shoulder bone of a bear you will penetrate to his vitals.

Here's my aiming tip: For the perfect H/L shot on a bear you wait until the near leg clears and aim for the opposite shoulder(broadside), this will expose his vitals and leave the most unobstructed path to them!

Quick question about your comment about your dad's 165 opening up quicker than a 150 NBT? Is this what you meant to say or is it the other way around, you would like something to open up quicker than the 165's? Not sure what bullet he is using but I will assume it is Seirra Game Kings BTSP, if so the ballistic tip in 150 gr will do similar possibly even more expansion as that is how it is designed. As you know I'm sure the BT has a polymer tip that upon impact is forced into the jacket to provide rapid expansion, thus opening quickly and creating lots of tissue damage. As such it isn't noted as the most solid constructed bullet in the world but if you aim for the lungs it is a deadly deer offering.