Chance your arm
Definition 1 of 1
Pro Tip 1/3Informal Usage
This phrase is informal, best used in casual conversations rather than formal situations. 
I might just chance my arm and ask her out.
Pro Tip 2/3British Origin
It's a British phrase, so it's more common in the UK, understood and used less in other English-speaking countries. 
When in London, I heard someone say they'd 'chance their arm' at the pub quiz.
Pro Tip 3/3Decision Point
Use it when someone decides to take an action despite uncertainty or risk. 
He's going to chance his arm on the new business venture.