Texture looks entirely too computer-generated and unconvincing. Every edge has the same amount of weariness to it and every bolt has a pool of leakage/rust around it. You'll want to break up details like that, make them only in logical places, if you want to achieve a realistic look. Also, the color of this ammo box looks a bit too desaturated to me, are you sure this is the right color for this asset?
I think you need to forget about Ddo and learn how to texture the "old fashioned way". You aren't going to learn anything using programs like that. There are tons of great tutorials out there if you look.
Like others have said Ddo is there to help but dont just smack on a custom preset and be done with it you need to play with the masks and materials. Also just look at some reference
Pay Attention to the edge wear and such, your is solid but on reference its minimal
http://www.thegnomonworkshop.com/store/product/873/Photorealistic-Texture-Painting I think is one of the best tutorials on the subject I've ever watched. It's very dated, but that doesn't matter because it explains in detail on how to reproduce realistic look and texture with photos, and how to think about the texturing in general.
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Pay Attention to the edge wear and such, your is solid but on reference its minimal
SuperFranky - Justin uses BodyPaint to aid in texture painting, the OP needs to keep it to just Photoshop.