Before installing this, take your version of the M4 from these links:

http://www.gta4-mods.com/weapons/m4a1-ris-f16469
http://www.gta4-mods.com/weapons/m4a1-sopmod-f15963
http://www.gta4-mods.com/weapons/push-tactical-m4-f14163
http://www.gta4-mods.com/weapons/m4a1-carbine--attachment-options-updated-f14032
http://www.gta4-mods.com/weapons/colt-m4a1-f13463
http://www.gta4-mods.com/weapons/mw3-m4-hybrid-scope-v2-model-and-textures-fix-f13154
http://www.gta4-mods.com/weapons/m4-sirs-sopmod-f7731