It depends largely on the composition, typical store bought ' lead cast bullets' expand a fairly good deal, that' s why we use them in moderate to low velocity arms, however, some hard cast bullets will barely expand even when pushed through the toughest of game, i.e. a .45-70 hard cast through a grizzly' s shoulder, I' ve seen one expanded only ~4% which is next to nothing. Hope that helps, it' s really vague, but that' s about as far as I care to dive into it at the moment, and with your question, I' m assuming this is enough.