If your putting enough torque to things to damage a receiver or shear an extension pin you are using waaaaaaaaay too much torque. No need for the Gorilla arm.
20-40 ft/lbs of torque is more than enough for a muzzle device.
Circuits is on the money by clamping the barrel, that is what the TM says to do but what if you can't clamp it?
A reaction rod or BEV block is the way to go.
And Hoser is dead bang correct. NEVER EVER use a crush washer on a suppressor mount or brake! Take the time to shim it.
Use Rocksett as a threadlocker.
Be sure to check your alignment before firing, if doing so visually be sure you see no shadows or crescents through the bore, you should see only rifling. Better yet invest in a Giesselle alignment rod or if your cheap, get appropriatly sized drill rod from McMaster Carr.