Extract this file in S.T.A.L.K.E.R directory. Usually is "Program Files\THQ\S.T.A.L.K.E.R. - Shadow of Chernobyl\"
This mod change the next weapons:
-Weapon Upgrades (Silencer, scopes, grenades launcher)
-Vintar & As Val
You can find all the weapons in this pack uploaded separately too. For the ones who don't want everything of the pack.