The Notebook star portrays a bumbling private investigator in the new film, alongside Russell Crowe as his enforcer, and despite previously appearing in 2013 mob thriller Gangster Squad, The Nice Guys marked his first time shooting so many scenes with firearms, while also performing a variety of his own stunts.

Ryan, who welcomed his second daughter with girlfriend Eva Mendes last month (Apr16), admits he was a little apprehensive about the prop guns at first, and he was constantly worried he would accidentally shoot a real bullet.

"I was kinda nervous doing the stunts; I've never worked a lot with guns, you know?" he explained on U.S. breakfast show Today. "I remember I wanted to shake every bullet... to make sure they were all fake."

In contrast, Russell was considered an old professional thanks to his stunt work in films like Gladiator, American Gangster, and Body of Lies, but he had to have a chat with director Shane Black before filming The Nice Guys to warn him his ageing body wasn't as tough as it once was.

He recently recalled, "I'm an old bloke now, and I used to pride myself on as many 100 per cent shots as I could provide for the director, and I still do, but I have a conversation with the director beforehand, which is like, 'You're dealing with 52-year-old tendons...'"

Meanwhile, Ryan reveals he was left truly impressed by Russell's general knowledge after spending so much time with him on set, especially after he managed to identify a string of world flags in between takes.

"There's not much that Russ doesn't know," the 35-year-old told Today. "One day, we were in car and we're bored and it's late, and we're in front of a hotel and there's, like, 50 flags (in front of the building), and he goes, 'Name those flags'... and I'm like, 'Who can do that?' And he goes (reels them all off) and he just nails them all."