Download SparkIV
Open weapons.img
C:\program files\ rockstar games\ GTA IV \ PC \ Models \ Cdimages

BACK UP THE FILE w_ak47.wtd!!!
Export w_ak47.wtd to back it up
Rename it w_ak47_original.wtd

Import the downloaded w_ak47.wtd and save the archive.

MAKE SURE YOU SAVE THE ARCHIVE

Now go kill lots of pedestrians with your new ak!

-GeNeRiC