Well, I just felt it was necessary to post this shottie because it is relatively easy to make and its a very fun weapon to have in your arsenal.
Step 1: Side Panel 1 / Internals
Step 2: Side Panel 2 / More Stuff.
Step 3: Barrel / Banding
Step 4: You Are Done.
You have now completed the BCS3 gun. Post pics of it in the comments if you make.