[sit-rep]

my question would be this...

If you fire a 45 in space... the bullet takes off and travels at it’s rated ballistic speed forever. How fast will you travel the opposite way??

[Skepolitic]

One of the fundamental laws of nature is conservation of momentum. So your velocity depends on the ratio of the inertial mass of your body, spacesuit, and 45 pistol to the inertial mass of the 45 bullet.

The conservation law is m1*v1=-m2*v2. Rearranging terms,

v1 = -m2*v2 / m1

where v1=your velocity
m1=inertial mass of you+spacesuit+pistol
m2=inertial mass of 45 bullet
v2=muzzle velocity of the 45 bullet

[Atlas Sneezed]

If you fire a 45 in space... the bullet takes off and travels at it’s rated ballistic speed forever. How fast will you travel the opposite way??

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About the same as if you were on earth and fired from a frictionless Radio Flyer wagon. In space, the most noticeable thing would be its causing you to rotate if the barrel axis was not in line with your center of mass.