Question: Just started using blender, and naturally the first thing I'm making is a minigun. It looks dope.

Problem is, when I applied the subsurface modifier, I ran into a problem.
[![enter image description here](https://i.stack.imgur.com/lZ9ZW.png)](https://i.stack.imgur.com/lZ9ZW.png)

And without it...
Nothing.
Any help is greatly appreciated.
Heres the link to the .blend files: <https://www.mediafire.com/?1iq489br01zej02>

Edit: It can be somewhat fixed by changing the number of subdivisions, but this makes it WAY to high quality.

Answer: 
I downloaded the model and found your problem. You've got hundreds or vertices on top of each other.

[![enter image description here](https://i.stack.imgur.com/FmZWy.png)](https://i.stack.imgur.com/FmZWy.png)

What you want to do is select everything live I've done and press `W` to open the specials menu and press "Remove doubles".

[![enter image description here](https://i.stack.imgur.com/hBrrk.png)](https://i.stack.imgur.com/hBrrk.png)

As you can see, you've lost all your sharpness in your mesh. You we're probably extruding faces to make these infinitely thin ones that gave you sharp edges, but there's a better way.

What you want to do when you find an edge you want to sharpen it select it and by pressing `Ctrl`+`E` to go into edge crease mode and sharpen edges by pulling your cursor from the edge's origin.

[![enter image description here](https://i.stack.imgur.com/g6qzn.png)](https://i.stack.imgur.com/g6qzn.png)
Here you can see I hot a little too excited and did a bunch of edges.
If you press `z` to activate wireframe, you will likely notice that there is a high density of triangles where you are seeing that phenomena. This is also probably why you see it get better/worse when you mess with subsurf's detail level.

You will have to mess with your topology in order for this to go away. It is otherwise a harmless effect. If you do your UV's well, you won't even notice when you finally texture the model.