It depends on what you are doing with it. The best place to start is with the same # grains as the caliber ( 50 in this case) and for target plinking that should do well. For hunting or longer range target plinking you will need to go up from there. I have used 70 - 80 grains for years out to about 120 yards, with an occasional 90 grain load for up hill or heavy brush. That all with a T/C New englander and patched round ball or mini balls. That should get you started, if you need more info, i have enough to make at least one of your ears fall of.
Typically 50 to 75 grains of ffG powder.
110 any more you just blow power out of the muzzle.
$50 to $150 is what I have found on line
Impossible to value a weapon with just the caliber and serial number to any degree of accuracy.
It is a Mountain Stalker. You should contact customer service, and get an owner's manual for your rifle. A .54 caliber rifle will use ABOUT 80-90 grains of black powder per shot. The exact load will depend of whether you are shooting round patched ball, Maxi-ball, or sabots.
Not unless you wish Blown it up & possibly injure or kill yourself. Smokeless powder has a much longer Pressure Spike, which puts more stress on the poorer metallurgical quality metal used in Antique firearms.
It is illegal to purchase or possess black powder for use in modern firearms like the Barrett M82. Black powder is considered an explosive and is highly regulated under federal law. It is recommended to use commercially available smokeless powders specifically designed for these firearms.
There were thousands of black powder guns made in Spain in any given year. These range from very cheap to well made. You did not give us much information to work on- whether it is a rifle, shotgun, pistol, or cannon.
The Hopkins and Allen MOD 34 is a Tennessee style blackpowder rifle. Not much to it a basic BP rifle good for beginners. Its worth about $50-$150 depending on condition.
Black powder is much weaker than smokeless powder. Smokeless powder, for this reason, once invented(much after black powder), replaced black powder in guns. However, black powder is still used in fireworks because the extreme explosive power of smokeless powder would prove too dangerous in fireworks.
Pistol or rifle? The ROUGH rule of thumb- start with the bore diameter. For a pistol, charge is 50% of the diameter- so about 16 grains of fffG. For a rifle, 100-200% of the bore- so 32-64 grains of fffG. You should check with the maker if they are still in business, and see if they have an instruction manual available. NEVER use anything but black powder, or a black powder substitute, such as Pyrodex.
Without a much more detailed description of your blackpowder rifle,I can only say between 100-150 dollars.If you want to resubmit your question,and include the overall condition of your rifle and the amont of original finish remaining I could give you a much better idea of it,s worth.