Great start. I do believe your allocating polys to things that don't need as much as they have. For example the screws and the barrel. This could be spent on some of idk.... Lens flair.... Good work mate, catch ya later.
I think the dustcover has a wrong shape. Its more rounded. Also, the way the stock is mounted at the receiver is different. Also it has no safety lever on the right side and the cocking lever is too small atm. You have some smoothing errors, too (the boxy thing at the right side for example) There are many missing details…