Welcome to the Forum.
You measure Pyrodex using the same powder measure that is used for black powder. Never weigh a powder charge of Pyrodex on a scale. It is much lighter per cc than real black powder but it packs the same power per cc as real black powder.
The maker intended it to only be measured by volume.
by the way, the granulated powder is exactly what you need. Do not try to use the pellets in your sidelock gun.
Hopefully you received a powder measure with the gun. These come in fixed or adjustable styles.
You didn't say if your Bobcat has a wooden stock or a plastic one and although I don't own one I've heard that the plastic stocked Bobcats are fairly light weight.
If your gun is one of these light weight guns I would advise that you shoot patched round lead balls. The ones to use in your gun will be .530 in diameter.
These roundballs weigh 223 grains which is a pretty good sized hunk of lead to be shooting but the gun will kick much less than if you shoot a heavier lead conical bullet.
The patches used for shooting roundballs should be either cotton or linen. Modern synthetic cloth usually does not work well at all (it can melt).
A good powder charge with either real black powder or with Pyrodex RS would be around 60 grains.
All muzzleloading guns have one or two load combination that they work well with. Finding the one your gun likes may take a bit of shooting and most folks start with a light load like 60 grains and take 5 shots. Then they increase the powder load by 5 grains and shoot 5 more shots.
By increasing the powder load you will find that at some point the accuracy starts to fall off. If you keep increasing the powder load some guns will have a higher powered load they like like 90 grains but it depends on the gun.
A 90 grain powder load in your .54 is a stout load that probably won't be used unless you plan on hunting.
A .54 caliber gun by the way is fully capable of taking any large animal in the U.S. except for a Grizzly bear.