Very nice scene.
I confirm that the barrel is much shorter ! I also have to tell you that these cartridges will not fit in the Thompson submachine gun !
45 Caliber cartridges are very short, and their bullets are rounder, and for what I know didn't exist in hollow point.
These cartridges were the same used in the Colt 1911 A1 pistol.
You can see the shells with actual proportions in the scene I made some time ago (rendered with Blender internal) :
http://3d-synthesis.com/33-Colt1911A1.html
For the Thompson 1921-1928 (your model is 1928), you can see it in animation at the bottom of the page below :
http://3d-synthesis.com/32-Thompson1921-1928.html
I had an old newspaper almost like this one, about Capone lawsuit, but unfortunately I lost it !
Keep on, it is a very good job ! I like the ambiance a lot !

French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.