Modeling of Guns/Weapons and its legal restrictions or intellectual property rights

Hi there,

I am almost in my final stages of completing a model of a gun which is modeled keeping in mind a specific brand of gun. I stumbled around this post on the internet of an artist getting into some kind of a legal trouble when he put a model of gun for sale but I have seen artists put up models of particular guns for sale here in CGTrader. My question is are we allowed to sell the models? Are there any legal restrictions? As an artist are we allowed to sell? I heard about tweaking the model a little to bypass them but tweaking it and making it into some sci-fi weapon spoils the charm of the weapon itself. So if anybody could enlighten me on this it would be very helpful for not just me but for the entire artist community.

Thanking you,

NV Media