What do you use to build your upper?

[Growler]

I wouldn't use a reaction rod with anything that used a crush washer.

Curious as to why?

I’m planning to use a Geissele reaction rod with my first build. I think this will be ideal for tightening the barrel nut as well as the muzzle device. When removing a muzzle device, the torque applied to the barrel extension would be in the same direction as needed to unscrew the barrel from the barrel extension, right? I would imagine the barrel extension torque would be close to 10x the muzzle device torque however. Has anyone ever had a problem unintentionally loosening the barrel extension in this scenario?