“Free Fire” stars Sharlto Copley and Armie Hammer and director Ben Wheatley held a press event on Monday at Stunt Ranch, a paintball and outdoor events venue just 17 minutes outside downtown Austin. Over barbecue and beer, the filmmakers answered questions about their gory, bullet-riddled action picture, set to release April 21.

On Wheatley’s reasons for developing “Free Fire.”

Ben Wheatley: I’d read transcripts about a shootout in Miami between the FBI and some guys who were going to rob a bank. The FBI had to write down shot-by-shot what happened, where the bullets were and what the injuries were. And when I read that, I was like, “This was really messy.” This was really horrible, and it went on for a long time, and they were all really highly trained and no one it seemed could shoot straight. Everything I’d seen in Hollywood wasn’t like that – everyone was an expert straightaway, and it was clean and choreographed. Not to say it’s a documentary, but “Free Fire” is kind of using that realism.

On setting the film in one room.

BW: It was easier (to shoot) because we didn’t waste any time in moving from place-to-place for location changes, but it was harder because if you make a screw up in the beginning – because we shot in chronological order – if you f*** up at the start, you don’t know about that until five weeks in when you find two characters are (positioned) really close to each other (when they shouldn’t be). So a lot of planning went into it. We built the set in 3-D in “Minecraft.” We had our own server we could go on and walk around.

Copley and Hammer on why they joined the project.

Armie Hammer: It was the creative people involved. It was a movie that you read the script and you go, “I don’t think there’s really been a movie like this in a long time.” It’s really fresh. I was a huge fan of Ben’s work before. To get to be in one of his projects was great.

Sharlto Copley: I was excited to work with Ben and, from talking to him, there was a chance to create a character with him and (screenwriter Amy Jump). Getting to play him as a South African – there’s not many characters like that, so I felt really grateful to be able to do that with him.

On the recipe for good one-liners.

AH: Good writing and good directing. There was so much material that we had. Also there was a really great collaborative atmosphere on the set where we would do it and then go, “Well let’s try one more.” We just kind of have fun with it. Everybody had a watermark of what they thought was good.

BW: We had a Darwinian editing style, where if you had more good stuff, the more shots you get in the movie.

SC: I don’t think of it in terms of a line. I love improv and I love being completely in the head of the character. In the case of (my character) Vernon, I was lucky because he has a big mouth, so he’s just spewing out stuff. During editing, they’ll choose a line, not necessarily everything you do. So you get pieces of a performance that feel more one line. I wouldn’t be able to think of it in terms of “try say something clever now!”