In some cases, 150 grains of loose and 150 grains of pellets are very close. But for instance, 150 grains of Triple Se7en 2f is about 120 grains of loose. Also a lot of time with loose powder, you have to be aware of your barrel length because if it is too short, you might not even burn all the loose powder off. Sometimes people report "flaming pellets." That is powder that never got burned off in the barrel.

Your Triumph is a magnum rifle. It can take 120 grains of loose powder with ease. It can shoot 150 grains of pellets with ease. I am sure with 150 grains of loose it might handle that fine. The question is, would there be accuracy?

Shooting loose, if you have good accuracy with 100 grains of powder, and you start moving up in grains and accuracy falls off, then you know that projectiles does not like the higher loads.

A lot of this muzzleloader stuff is hit and miss. You take a projectile and you see how hard you can, or want to push it.