Over the years there hasn't been a whole lot of discussion about stinging streams. I was reminded of this lately when taking a shower with a different shower nozzle setting. This setting stung quite strongly, which caused me to recoil. That was when I got the idea to apply this to water wars. For the amount of water output, the stopping power was quite strong. Unfortunately you probably need to be pretty close to get this effect, but it's still worth looking into.
The XP 110 is well known to have a stinging stream (iSoaker review, Aqua-Nexus review). The XP 105, XP 150, and SS 40 also were noted on iSoaker to have stinging streams.
Are there any other blasters which I'm missing? I'm somewhat surprised that there are no reports of stinging streams for the CPS based blasters with smaller nozzles. Maybe the pressure is not high enough.
I might do some tests to figure out what makes a stream sting. The basic recipe seems to be relatively high pressure combined with a small nozzle. I couldn't find a whole lot in the medical literature about this in particular, though I could find plenty on what it takes for a water jet to break human flesh. We are nowhere near that point, thankfully.
Edit: Apparently the XP 110 has a nozzle diameter of about 0.0625 inches and a pressure of 40 psi. I might be able to use this to make a rule to estimate when a stream will sting or not.