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.
Black powder is not suitable for use in a Barrett M82, as it is a modern, semi-automatic rifle chambered for .50 BMG ammunition, which uses smokeless powder. It's important to use the appropriate ammunition for safety and optimal performance.
$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.
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.
Black powder and smokeless powder differ significantly in power. Smokeless powder is more powerful, providing higher velocities and energy compared to black powder. Smokeless powder's cleaner burn and increased efficiency make it the standard propellant for modern firearms, offering better performance and reduced fouling.
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.
50-75 grains
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.