Hello there imperial civilian!
This here is the finest semi-automatic self-propelled bolt weapon available to man! though it may need supports in some area's (like the front barrel) it is otherwise completely normal (oh, and it also doesn't fire anything. That right only goes to the REAL space marines)
just print it out on your hand-dandy forge world (or printer, whichever is available)
feel free to contact me with any problems or suggestions.
also, this hasn't actually been printed (school won't let me print it because of their restriction on things that look like guns, so if you make one, please post pics!)
For the emperor