No. Not only will accuracy be worse than a thrown rock, it is potentially dangerous. If the bullet moves forward before firing, it will leave an air space between the powder charge and the bullet. This is an established way to blow up a muzzleloader. Use the right sized bullet for your rifle.
Yes, but only if the bullet has the proper sabot. The sabot essentially acts as a spacer between the bullet and barrel. This is commonly done to drive lighter bullets to higher velocities, but the longer of two bullets, weighing the same, tends to be more stable as well.
4/100's of an inch. .50 cal = .5 inch .54 cal = .54 inch
50-150 USD
Take it to a gunsmith. That is what they do.
1/4 mile and then some
50-75 grains
ALOT
they both shoot far but the 408 is more accurate and even stronger than the 50 cal but to answer the question the 408 shoots further.
They will "fit" but they will not fire correctly, and will break when the bolt tries to push two of them at once.
50-300 USd
I havenever heard of a .54 cal but no, a bullet that will not stay in place for the striking pin will not fire, DO NOT TRY IT, if by some off chance that the striking pin hits the firing cap then the bullet has already started its trajectory at an angle and will probably damage the gun and yourself, it will be hard to find but you may be able to find a a saboe for that caliber, but you may just want to go buy some .54 cal ammo...
There is a .50 replacement barrel on Gunbroker.com
it depends what type of marker you are using 99% percent of the time it will be .68 cal but you can find .43 and .50 cal markers.