i dont model from concept art a lot but the times i have, i realized half the time the lighting doesn't even make sense. So you have to go with your own intuition to, not just try to match pixel for pixel. Go with what you think will look cool and capture the feel of the concept.
Don't trust concept art perspective to be true all the time. It may lie to you.
Anyway, I think what's important is breaking things down. Dumb advise but it's just true.
On this asset I don't think it curves on this plane
Your's droops and curves, I think it's way more planar. I also don't think it sticks out from the side of the gun as far as you have it. Sorry don't have much advise, imo it's just a case of trying to understand some planes and relationships with other parts and then developing from there.
Exspanding upon zachagreg's well thought out examples that really is a key aspect to think about or in other words pre-planning prior to modeling anything, will mostly mitigate potential problems from occurring, any how a few additional points to keep in mind:
1. Where possible I'd advise at this stage to mainly model off references, rather than using a free style 'eyeballing' method which requires a ton of practice and experience to capture a near enough copy of the subject so for this exercise I drew a 'blueprint' from your posted pics upthread and analyzing the main shape we'll start with a plane:
2. Now couple of things to note, if while sketching your model extra edge loops are necessary to outline a detailed profile, then by all means add them, because sufficient geometry is a main consideration to support a well designed topology, well at least from my experience. Also transformation action constrain too axis will confine either vertical or horizontal segments alignment, therefore minimising mesh surface 'peaks and valleys' a typical cause of shading artifacts.
4. With the mirror modifier applied and we'll then validate/check that our edges are properly aligned along their applicable axis then hopefully the object should as expected shade correctly once sub-divided (lvl 3)
5. In my opinion seems fine plus importantly via GI preview mode, no noticable shading problems.