Welcome!
150 grains is definitely not necessary. In fact, I have never gotten any of my guns to shoot accurately at 150 grains (or its 777 equivalent of about 130 grains). I use 110 grains of 777, which is worth roughly 130 grains of Pyrodex or blackpowder. I hunted previous to this season with the standard 100 grain load. When I started muzzleloading, I have 6-8 very successful seasons with 85 grains pyrodex at ranges up to 150 yards. You don't need to obliterate the deer to kill it :lol:
The first thing is to find a bullet and powder combination that your gun likes. Surprisingly, muzzleloaders can be VERY finicky about what they will shoot accurately. At 100 yards a gun might shoot 5" groups with one bullet/powder combo but 1" groups with another. So the first thing to do is make sure your gun will shoot the bullet you want accurately. Best thing is to start at 80 grains of powder and work your way up until accuracy suffers (or you reach your desired powder charge and recoil, whichever comes first).
If you are thinking of shooting over 100 yards, I suggest you shoot your gun fairly frequently. If you are thinking of shooting 150-200 yards, you are likely going to need to put at least 100-200 rounds through the gun each year to keep your skills up and be able to shoot tight groups "out there" (the more the better). Once the gun is sighted in I suggest shooting as often as possible under field conditions, ie no bench and just the support you'd expect to have in the field. One of the hardest parts about long shots is KNOWING the range, since the bullet is dropping pretty quickly at 150-200 yards and a mistake in range estimation could lead to a miss or wounding. I have a laser rangefinder; alternatively, you can practice a lot and see how you do estimating, or pre-measure landmarks from your stand.
Good luck!
