Can your muzzleloader bullets be shot with 150 grains of black powder or a blackpowder subsitute?

  Yes, if your muzzleloader manufacturer says it is safe to do so.  However, just because your muzzleloader will allow you to shoot 150 grains of black powder, does not mean that is the best load to use.  In most shooting situations the first imperative is to hit where you are aiming. To accomplish this you will need to use a load that your muzzleloader likes.  This is not automatically going to be 150 grains with every bullet you choose to use.  The question that really needs to be answered is what load will give me the best possible accuracy at the distances I will be shooting and still have enough kinetic energy to get the job done?  That can only be determined through testing different weights of bullets with different amounts of powder until you find that load that is both accurate and lethal.

  Which of your muzzleloader bullet should I use?

  This question requires additional information to answer it correctly.  What rate-or-twist does your rifle have?  At what distance will your average shot be taken?  What game will you be hunting?  Are you more concerned with weight of bullet or a flatter trajectory?  A good place to start is by determining which weights of bullets generally perform well in a rifle with your rate-of-twist.  Of course the lighter the bullet the flatter the trajectory.  Since not all muzzleloader are made exactly the same, most of the time different rifles even though the same brand, will shoot the same bullet differently.  To find the best bullet for your rifle, in the approximate weigh you are looking at using, requires testing each bullet weight with different loads of powder to see how well they will perform in your rifle.  This results in finding the bullet that your rifle likes the best.  Although your rifle may shoot most Precision Rifle muzzleloader bullets into a 2 inch group at 100 yards, you would like to find that special load that shoots into the same hole every time.  This of course is the best bullet to hunt with in most cases.