Not sure of the sure of the size - but you can go to a store that carries welding supplies and pick up a small tool of 'torch tip' cleaners they run about $5 and have many different sizes included...
Should be .027", they do wear, so it coud be a few thousandths bigger than that, depending on how many shots you have through it. Just be careful with the torch tip cleaners, you could be opening up your flash hole prematurily. I NEVER use an abrasive pic in the flash hole, always use a wire nipple pic made/marketed by T/C.