It may not be cut out, but it's all down to how it looks. I mean the main body of the gun is flat, the barrel is flat, the sight and the bit under the barrel is flat, everything is flat except for the spinny bit. In a FPS view for example, it would look like a cut-out with a extra cut-out hammer bit.
I'm not having a go, because that's exactly how I make guns, except I tend to use cylinders more. Maybe next time you could try making a shotgun, something with lots of cylinders but also these flat bits. I don't advise trying to make your own gun designs just yet, try to replicate a real world gun as much as you can, otherwise you simply make exceptions. I think that replicating real guns forces you to add detail, because if you were to start with a simple cut-out, you would see the details in the photograph/texture, like safety levers etc, and be more inclined to add them. Starting with a cut-out is often the best way, it's what you do with the initial shape that makes the difference.
Take the barrel again for an example, having a non-round barrel is fine, but a square is probably the worst choice for it - it does look like it's trying to be round, and there's no conceivable reason we can see why it isn't. If you are using a non-round barrel, maybe make it rectangular, or better yet, go for a coffin shape, so it looks like the barrel is angular for the sakes of stability. A lot of hand guns have weird shaped barrels, but the design has to qualify this, there has to be a reason why, and I can see how that would be tricky with that particular gun design. If you extend the support part under the barrel so it goes right out to the end of the gun, I think it would look more convincing, more obvious that the barrel is deliberately like that if you know what I mean.
Some gun models can be incredibly complex, M16's and Carbines for example can have lots of fiddly detail, good for practice but they take time, I think shotguns are great practice, they're more accessible if you know what I mean, it's a lot clearer what goes where on a shotgun than some other weapons.
