I came accross an interesting write up on a German site, Babel fish translation:- .. the C25 contrary to the C20 however a special value within the CO2 10m pistols gives is it vertically under the run of attached CO2 tank. This is favourable, since the liquid carbon dioxide always is when shooting at the ground of the receiver and the gaseous collects itself over it. With a horizontal attached cartouche the liquid CO2 can perhaps arrive when shooting up to the valve, which can impair the accuracy of the weapon. Besides so also the gas consumption sinks