Be a little bit in more dept with what exactly you did, first of all i didnt download the scar but, either u gotta unject it to the normal .rez or it is a rez.. take the old rez file and put it somewhere useless for whenever else u will need it, and then rename it to .rez instead of the .reznew it is
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I now see what your choobbieness has done, it comes as a injectable, you need to get rezinject and inject it into GUNS_M_PV_AR.rez, after that it becomes a reznew file, after that take the original and put it somewhere else.. And rename the reznew to rez and your done, NEXT TIME READ THE FUCKING STICKIES!!!