Also I've designed a very simple but effective ABT. It's a ratcheting system that will lock the mechanism at any point, so if you cock the barrel halfway and your hand slips off (I'm sure everyone has seen this happen) the mechanism will lock and the barrel will stay where it is. Or if you accidentally pull the trigger when its fully cocked, nothing will happen. The mechanism doesn't unlock until the barrel is fully returned to the breech.
Not sure if any other break barrels out there have a 'true ABT' like this or just trigger blocks?

Pro's - 'true ABT' at any point in the cocking cycle. Additional layer of safety
Con's - Can't be de-cocked. Adds roughly 25mm to the overall length of the action.