Install:

-Add files to gta3.img.
-Find: "335, knifecur, knifecur, null, 1, 50, 0" in default.ide.
-Rename "knifecur"s to "stungunvc"s.

Gun is installed.

Adding it as a new weapon:
-Watch Ryosuke's tutorial on Youtube.

csillam_faszlama