These don’t provide a perfect fit for published weapon stats, but they are fairly close in most cases and probably good enough for gaming. The damage is a better fit than the range, which is fortunate because in GURPS damage often matters more than range, with few engagements happening beyond half damage range.
You will need to know the projectile diameter (or ‘caliber’, which we will call c, measured in millimeters), the projectile mass (bullet weight, in kilograms, m), and muzzle velocity (in meters per second, v).
You will also need to know the kinetic energy (in Joules, k) of the projectile at its muzzle velocity, but you can calculate that from m and v:
k = m × (v^2) × 0.5
Damage (in dice, d) can then be calculated with:
d = ( (k^(1/2)) / (c^(1/3)) ) × 0.23
½ D Range (in yards, h) is:
h = (m^(1/2)) × (v^(3/2)) × 2.5 / c
Finally, Max Range
(in yards, r) is:
r = ( (h^(1/2)) × 120 ) + h
To make things easier, here's a Google Docs spreadsheet which does all the calculating for you (including converting bullet mass from grains to kilograms).