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I have a Radical Arms barrel and no problem with the extension. The one I read recently with the extension coming loose put the barrel in the vise when torquing the barrel nut.
I don't understand why someone would put the barrel in the vise instead of the receiver.
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The only reason I can think of for doing that would be if you didn't have an upper receiver vise block. Otherwise, it makes no sense for torquing the barrel nut, and puts a very high load into the aluminum notch in the receiver (much higher than torquing a flash hider).
However, I got the impression that unscrewing the barrel extension has also happened when removing gorilla-tight or loctited flash hiders and reacting the torque through the barrel extension locking lugs. Even a really tight flash hider shouldn't be anywhere close to the torque of a properly torqued extension, but if the extension dimensionally expands during the high-temperature meloniting process, I can see how it may lose it's installation torque. Theoretically, the "best" way to react torque from the flash hider is to remove the handguards and gas tube, and use a barrel vise block to grab onto the barrel itself. Unfortunately, with the popularity of long freefloated handguards, that can be a lot of trouble just to replace the flash hider.
Presumably, since these barrels are stainless steel and are not melonited, they
should still be torqued to spec, but I suppose until someone intentionally removes one with a torque wrench, we have no way to know for sure.