You have 29 colors. Those greys could easily be reduced. You might want to think about that black line art, it's harsh and your colors aren't particularly high contrast.
I'll make an edit later.
EDIT:
You need to have an eye on your palette. 29 colors is unnecessary, you had a few colors that was only one point higher in value. The difference was almost unnoticeable, it was pointless. A lot of the shapes on the metal body of the AK didn't make sense, even in context the shapes didn't make a lot of sense. It's my opinion that the black lines make pixel art look flatter than it is.
I think it's important for me to mention, if you have a reference you used then it'd be in your best interest to post it or the link. This will help us know what you're trying to achieve.
I liked making those black lines a bit softer with anti aliasing. I got rid of a lot of colors. 13 actually. Look at this, if there's anything you like feel free to learn from it. Anything you hate you can reconsider and if you still hate it then don't use it.
Hope this helped you out.