SO COOL YOU GOTTA MAKE IT! You're minifig will love this for his birthday or Christmas!!! Pros: Removable barrel mag. Optional bipod. Cool looking. Doesn't use many pieces. Cons: Uses one minifig hand.
Step 1: Get Stuff
Just look at the pic...
Step 2: Build Parts
I forgot to take the pic of the finished drum mag. Sorry!
Step 3: Assemble the Gun