Looks like a good start, now finish it.
You're missing quite a few details, though the worst offenders are the stock, receiver, pistol grip, and magazine. The pistol grip is probably the most glaring, as it looks really flat from the side, and needs the characteristic "fang"-shaped bump that's present on the weapon. It doesn't need to be too pronounced, though, as you can accentuate it by a texture later on (but I wouldn't do it as a floater).You need to detail your receiver more, this should be easy to do with a mix of unattached geometry and baked floaters.Your stock needs a lot of detail. If the full HK417 stock seems too intimidating to model, don't be afraid to substitute it for another equivalent stock, most people won't notice/care even if the stocks might not be interchangeable irl.If you can texture/render a see-through magazine, awesome. If not, consider looking at steel magazine designs, or at least add some kind of crease or taper in the magazine so it looks more believable than a flat, curved box. If you keep it as plastic, I would chamfer its edges more.