Might be a silly question but I was wondering about how much air a PCP uses v a springer.

For instance if a PCP & springer both produced 11.5 ft/lb & the springer has a known cylinder length & diameter the volume of air behind the pellet can be calculated. With a PCP a 'dose' of compressed air is released from the reservoir but what volume would this 'dose' of air occupy at the same temperature & pressure as the air in the springer?

Does one type use more air than the other to achieve the same result? Any fluid mechanics, physisists, or theorists got any ideas?