They had a cardboard box in my high school chem class, that was the volume of one mole of gas at STP, it was a pretty big box to fit in a syringe, as you can figure for yourself. So yes, you'll want to scale down. Question, the output of the reaction will be moist hydrogen released from aqueous solution, how would you compensate for that? (I ask the question this way because a similar question has come up lately -- partial pressure of water vapor) There will also likely be come HCl vapor contamination, so you'll have to plan for that.