It's still pretty cartoony! Try to take the material into account to really sell it, plastic and ceramic both tend to be pretty glossy! Play around with some references like this:

Play around with the reflections!

Hey I made a edit and made parts bigger so detail would be more applicable. I added shading as well. A tip would be to find a good reference and try and mimic where the lighting is on it.

P.S Use a png background next time.

I want to point out that Dylan's edit is less reliant on outlines than the original. While outlines can be useful as a stylistic tool and to help separate sprites from busy backgrounds, in pixel art they often take up space that you could be using for detail. So, when adding details, try to avoid doing them with lines, and instead create them with light and shadow. Add outlines later if they're still needed.

Hey this is really good for starting out. Some easy improvement might be:

- instead of black outline use a dark grey, as it's contrasting very strongly
- increase the contrast on the gun. you have a couple of greys that are very similar and a couple of browns that are very similar. I'd make them more different in value (darkness).

The silhouette of the gun is very good and it is reading clearly and accurately. Your main focus should be improving the form inside the outline - getting the shapes to read well. To do this you will need to do research into lighting / light sources and clearly pick a light direction for the piece.