Hey @brianbuckman,
I think its undesirable to have intersecting mesh in a game asset because of shading and lighting artefacts.
I would also say that being a weapon that will be close to the camera, the lower quality of modeling would be noticeable.
There are probably more reasons than this, perhaps @jlampel would be the better person to answer this.
There are several courses here on CGCookie that will assist you with game assets,
There is a series of courses for creating a FPS weapons,
Modeling Weapons for a First Person Shooter
Texturing Weapons in Blender and Substance Painter
Rigging a Transforming Rifle in Blender
Animating First Person Character Weapons in Blender
Also there are courses like,
Animated Sci-fi Game Environment Creation in Blender
Creating Mini Tanks for a Mobile Game with Blender
Game Character Modeling with Blender
Hope this helps!
