Adding final details

At this point, the gun is really starting to take shape. Let's add a little more detail to finish it up.

A great way to add detail (without too much work) is to run loop cuts across the existing faces, and then scale these new edges in by pressing Alt + S. This gives the appearance of a panel line or cut between different the portions of an object:

You can also create one such cut, and then rip the center edges. This will enable you to create a second line or cut that doesn't go all the way across the geometry:

Here, we'll create some additional vents for fins by picking a series of faces on the upper barrel and eliminating them:

Then, we can pick the two edges at the top and bottom and fill in a face. With a series of loop cuts across the face, we can easily create our fins:

We'll continue the detailing by adding a series of basic shapes to our gun:

Then, using techniques that we've already covered, you can go ahead and detail these small pieces. Here's an example of one small piece on the side of the gun's body:

If you'd like, you can look at some real weapons for inspiration. Otherwise, feel free to get creative!