If you're into self abuse, here's the whole formula.

I=(WbxV+4000xWc)/225,400

Where: I=impulse (lb-sec)
Wb=bullet wt (grains) you'd want to include the wad
V=muzzle vel (fps)
Wc=charge wt (grains)

Then plug that into Vg=32.2xI/Wg
Where Vg is gun velocity (fps) and Wg is gun wt (lbs)

Finally Eg=Wgx(VgxVg)/64.4
Where Eg =free recoil energy (ft-lbs)

If you're completely confused, congratulations!
Pete