how is it so hard to find an armourers wrench that fits this thing? — 3 Answers

The tapco wrench fits it perfect. I know it’s discontinued, but if you have one laying around and wondered if it fits, it does.

Having recently suffered the same frustration, I can confirm that the Wheeler Delta Series Basic Armorer's Wrench will do the job. Note that it should be the "basic" wrench with the bilaterally symmetrical, straight profile, like the one included in the combo kit linked below. Wheeler also has a "professional armorer's wrench" with an asymmetrical, more curved/diagonal profile, but that one appears to have too many pegs to fit into the holes on this barrel nut.

Combo kit with the right wrench: https://www.opticsplanet.com/caldwell-wheeler-delta-ar-combo-tool-with-torque-wrench-156700.html