+1 on Zi0's crit. Right now it looks like your images are just screengrabs from Max/ Maya? I wouldn't recommend that for texture crit because those flatten out the lighting. Instead, try to light your scene properly or download the trial version of Marmoset Toolbag. Really I just want to see some material definition.
Also, it looks like your rust isn't following any form of the gun, but is rather a "splotchy rust" pattern that was applied over the entirety of your UV sheet? Keep in mind that guns are finished to protect against rust but scratches remove the protective finish and expose the base metal. Also, scratches generally happen on edges. Pooled moisture can speed that erosion process up as well, which would occur in crevices. I'd try to avoid rust textures that are just rust on an untreated metal as no gun is untreated.
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Also, it looks like your rust isn't following any form of the gun, but is rather a "splotchy rust" pattern that was applied over the entirety of your UV sheet? Keep in mind that guns are finished to protect against rust but scratches remove the protective finish and expose the base metal. Also, scratches generally happen on edges. Pooled moisture can speed that erosion process up as well, which would occur in crevices. I'd try to avoid rust textures that are just rust on an untreated metal as no gun is untreated.