How fast will a bullet travel if fired in space? .50 cal for example.?

The answer is, there would be no measurable difference between firing the gun at sea level or in a hard vacuum.

At sea level, air pressure is 14.7 PSI, in space it is of course almost 0 PSI (you need to get out between the galaxies to get to a true hard vacuum.)

The pressure in the bore of the gun is between 45,000 and 52,000 PSI depending on the loading. Any difference in the speed of the bullet will come from the difference in pressure on the cartridge and muzzle sides of the bullet.

The ratio, using a 50,000 PSI loading would be: 14.7 / 50000 or 0.0294%.

There are so many more variables that would affect the bullet speed to a greater extent. The temperature of the cartridge would have a much greater impact. The small variations in the powder charge would have more impact.

Again, there would be no measurable difference.

It would travel at the rate the gun powder ignites. Around 1100 fps minus a little friction from the barrel.

It would make very very little difference, a foot or two of air doesn't significantly slow a bullet. A bullet in flight loses less than 2fps per foot travelled, so two feet of air in the barrel would slow a bullet by less than 4fps. Most bullets have a muzzle velocity of 2000 fps or greater, so an extra 4fps is trivial.

A typical muzzle velocity for a .50 caliber weapon is around 2,000 feet/second (..2,000 mph..) Depending on the weapon itself and the load of the round, that would be the bullet's velocity in space. Of course it will travel much, much farther in space since there's no air resistance.

Approximately 1100 FPS (feet per second) but it would travel faster due to lack of gravity in hard vacuum/

I would think it would travel at the muzzle velocity for a loooooooooooooooooooooooooooooooooong time.

really fast because there is nothing in space to slow it down, like friction

it would not travel faster it would just keep on going because there is not friction