It depends on the game so I can't guarantee that what I'm gonna say works for MW3, but here we go:
First, find out where the ammo address is written to(find the ammo address and use "Find out what writes to this address" on CE). The function you'll get as a result usually is the one that handles most, if not all, the gun related stuff.
Start to place breakpoints inside said function until you manage to freeze the game every time you shoot.
Now, this last step may cause a lot of crashes, but you can start to NOP out any calls to other functions inside that function. If you see that your weapon then has No Recoil, congratz you found the recoil function.
PS: Watch this series of tutorials here