Take blaster weight, for example: Above is a chart showing all the stock water guns I have numbers for (total dry weight only). For those with keen eyes, you should be able to read the blaster names beside the bar representing its weight in grams. Before plotting this, I had considered a decent dividing line being a Super Soaker XP 70 being the largest of the small-class blasters and the CPS2100 as the smallest of the large blasters with thing in-between the XP70 and CPS2100 to be considered mid-sized. Interestingly, this ends up mostly working out to having weigh cutoffs at 500g and 1000g (though, interestingly, the XP70 actually weighs a little over 500g coming in at 560g; I think they used thicker plastics back then).
Not surprisingly, the heaviest blaster is the Monster XL followed by the Hydro Blitz and the CPS3200.
All that said, I'm more convinced of classifying blasters 500g or less as light, blasters above 1000g as heavy, and 500g-1000g as mid-weight. There are some exceptions to this rule such as the XP70 which is a little heavier than its size suggests. However, these weight groupings seem to work well for the purpose of then comparing output and capacity levels upon.
