ar tools ?

[LRRPF52]

Don't use a reaction rod installing a flash hider. Use a barrel clamp.

May I ask why?

Because you are now placing torque on the barrel and barrel extension, not just the barrel.

Anytime you're doing muzzle device work, clamp the barrel only, never the upper receiver.

A common principle in tool use/applied physics, is to isolate the work to the parts being worked on, without introducing other components into the mix.