We can't really answer that until we know WHICH 45 and which 50. In the case of a muzzleloading black powder rifle, the .50 with have more energy, all other things being equal. However, it could also compare a 50 muzzleloader to a .45-70 cartridge rifle, which is more powerful. Caliber alone only tells us the width of the bullet.
It depends on the load
yes
The .45 caliber bullet is not used in a sniper rifle.
trade it in for a 45 caliber
Yes
Depends on the load
Depends on which 45 and which 44 chambering you are talking about the load
100-400 USD
Shiloh Sharps caliber 45-110. Nice rifle, huh?
Impossible to answer without the sn and maker.
no, a 45 caliber is way more powerful than a 40 caliber Actually, it depends. The following is copied from another answer of mine: The muzzle energy from a .45 caliber round can vary between 350 to a little over 500 ft-lbs, with velocites from about 850 feet per second to over 1000 FPS. The .40 caliber round can range from about 480 to about 570 ft-lbs of energy with velocities ranging from about 1000 FPS to about 1400 FPS. So, in short, it depends on the specifications of the particular cartridges you are comparing.
As far as self defense handguns go, the .45 ACP is an extremely powerful and effective caliber, with a proven military track-record.