listen. download this file. then just drag it to desktop. then, go to your AVA folder/AVAGAME/weapons (wrong i know but its example) and there you'll find files that are UPK format.
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what is upk? upk is almost same as .rar. so, upk files include files that can be edited and this is the way to skin / mod AVA weapons,...
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Copy one of files and paste it to desktop. then drag the .upk file into this program. BOOM! in same map as your upk extractor is (let's say desktop) there'll appear MAP!!! in this map you'll see 2Dtexture files and some other sheet.