Make backups of your original files before replacing!!!!!!!!!!!!!!
While using Open IV replace files:

"WeaponInfo.xml" goes in \GTAIV\common\data

All guns/weapons models are replaced in GTAIV\pc\models\cdimages\weapons.img\

"gun@eagle" goes in GTAIV\pc\anim\anim.img\
(dont use this anim for EFLC)

If you want a better desert eagle sound download my main IV weapons back to attain the audio file 
https://www.gtainside.com/en/gta4/weapons/126557-hd-iv-weapons/
