Ensure that you replace the PSG-1 for the mod to work.

First, with SparkIV, export your WEAPONS.ivaud from resident.rpf (find it in
pc\audio\Sfx). Open the WEAPONS.ivaud with GTA IV-aud and import all sound files
to here (match the names):

SNIPERRIFLE_SHOT1_L
SNIPERRIFLE_SHOT1_R

SNIPERRIFLE_SHOT2_L
SNIPERRIFLE_SHOT2_R

Save once done and import back to resident.rpf, Save and close.

Open weaponinfo_for_fnfal.txt file and replace the weapon line in it to Sniper
Rifle line.