For any sci-fi action film, the look of the props, specifically the weapons, often dictate the feel of the universe in which it's set. For "Looper," out this week, director Rian Johnson had a vision for the guns used by Joseph Gordon-Levitt, Bruce Willis and the rest of the cast. They reflect his futuristic world, where men kill people from the future -- including their older selves -- for money.

The weapon of choice for these Loopers, as they're called in the movie, is the blunderbuss, a gun that harkens back to the Old West model in name and function. When it came time for prop master James Kroning and his team to make Johnson's blunderbuss a reality, it took several revisions to find the right balance of old and new.

"The way it all boiled down was I started looking at the script as futuristic, but then the first thing that we were talking about was the blunderbuss. [Johnson] wanted the diameter of it to be pretty big, so it looked like it was an explosive shell that came out of it, bigger than just a normal shotgun," Kroning told MTV News. "We get the pieces together. The production designer and I played around with configurations of it, and then we were showing Rian ideas, trying to give it a little polish, but he was resistant to the polish. Every time we tried to show him something a little slicker, he'd pull back and go, 'They made it in the back room.' "

To find the right look for the blunderbuss, Kroning took a step back and let go of the idea that most futuristic guns look pretty. "Eventually, we came around to the look that he wanted, and then I had the prop house put it together and they still wanted to make it really shiny and bright," he said. "Basically, before I showed [Johnson] the finished one, I said, 'Ok, you guys really need to dirty this thing up. Drag it through the dirt. Stop being so precious about it. Make this thing look like it's this completely beat-up, utilitarian item that is just kind of dreadful.' Once they got that to him -- mind you this is after probably four or five rounds of illustrations and mock-ups -- [Johnson] was like, 'You nailed it.' From that point forward, I knew what he wanted the general vibe of the props."

How did Joseph Gordon-Levitt become Bruce Willis for 'Looper'?

Loopers weren't the only characters in Johnson's movie that needed arming. The Gat Men, a gang of enforcers for the mob, live up to their name in reputation and firepower. For them, Johnson wanted a more polished, professional look than the Loopers.

To find just the right gun for the Gat Men, Johnson went with Kroning to an armory that contained somewhere between 20,000 and 30,000 weapons. "[Johnson] wanted to Gat Men to have something that we've never seen before," Kroning said. "This company made this BFR, they call it. It's a .45-70 caliber pistol. It's effectively something you'd hunt elephants with. Rian fell in love with it immediately because it was beyond 'Dirty Harry.' "

For one Gat Man in particular, Kid Blue (Noah Segan), Johnson had a special look in mind. As a kind of futuristic cowboy, Kid Blue got a modified version of the BFR, which reflected his character.

"For Kid Blue, we wound up retooling [the BFR]," Kroning said. "[Segan] wanted to learn how to spin the gun western-style, so I hooked him up with a gun handler, and once a week, he would go have lessons. Spinning that gun was no easy feat. He trained for that thing for two to three months. By the time that we were getting ready to film, Noah would come to work, and he had bandages all over his hand."