First weapon feedback/help

so, i am working on a weapon animation, and figured this would be a good place to get feedback/help. this is only for fun as I try and learn the program, so not a serious project. I also apologize if this was brought up before, but in my searching the forum, i could not find an answer. any general feedback on the look of the weapon is also appreciated!

so, this is the LMG before I render it, in its solid form and all (2nd image)

But after I click Render Image, it changes.

Is there a way to prevent this? or will I have to model with this in mind?