I've had arrows get broke on elk when it is a quartering away shot and the far shoulder is hit. The arrow stops in that far shoulder and then when the animal runs the arrow backs out and the near side leg shears it off. That big shoulder blade rotating back and forth makes short work of breaking an arrow. I'd bet when you shot the moose its initial lunge to start running made the arrow back out most of the way and then its near side leg just sheared it off. Happens pretty often when the arrow stays in the animal and it tight in behind the shoulder (like we all hope it will be!). Trial153's arrow weight suggestions for type of broadhead being used are setups that I'd hunt with confidence. Good solid advice.
