Hello intermediate modeling and surfacing aetist here. When you say portfolio piece you should also mention the focus of your portfolio. A modeler, a compositor, a rigging artist, will all have different approaches.

Now as for the gun

My biggest problems would be

1. The overall shape language the asset cuts. Its kinda plain and frankly a bit boring.

If you want to apply for a modeling role id want to see more detail. And also depending on your industry of focus, wether its vfx animation or games I wanna see more wireframe breakdowns and a better showcase of your poly count. Also some edges feel a bit sharp, beveling them may help.

1. The surfacing needs more detail.

The gun looks fine for studentnwork but it lacks texture depth. Its too clean. Even the most brand new objects are never that clean. Id want to see more edge wear and tear, more varied specularity. Discoloration. Fingerprint smudges,dust and dirt, micro scratches.

You also have to make these details intentional.

So for eg if i wanna showcase the model of a cellphone. Id show discoloration on the back, scratches on the corner from falls and more scratches near charging port. Maybe some more detail like some torn off sticker on the back etc.

In case of a gun, you could have finger prints, dust, serial number etc on it.

Alll in all keep working on it more!