If I can have an intuitive stab at what Johns saying (to see if Ive got the gist):

With a pneumatic axe, the amount of energy imparted to the weapon before impact is independent of its weight (and presumably depends on the energy of the air expanding in the cylinder), no matter the speed/weight trade-off.

With an electric axe, the more weight is present for a given sweep, the longer the motor will have to impart energy to it - and therefore the more energy the axe will have on impact.

i.e. a pneumatic ram imparts a given amount of energy regardless of how long it takes to expand, whereas an electric motor imparts energy (potentially) proportional to the time its running - with provisos about efficiency, variable gearing, etc.

Did that help, or have I just muddied the waters? (Its one of those things which could make sense, but could easily *not* make sense, too).

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Fluppet