So a while ago I was talking with a guy who said he used a reaction rod in his assemblies until...
he had a stubborn upper/barrel. He brought torque to the nut as usual, but despite loading and unloading the nut a few times he just couldn't clock the nut right and when he did, the front sights were canted!
WTF!?!
So he disassembled the barrel/nut/upper and found that while the reaction rod had held the barrel, the nut had exerted enough torque on the upper that it cupped the slot the slot in the receiver cut for the barrel indexing pin!
I'm not certain that this was the result of incompetence or a real issue (although my last build was stubborn to get to align and I'm tempted to break it down one more time to see if I was fighting that same dragon. My sights are not canted; so there's that
)
And I think the development of the BEV Block might hint that this is more common than one might think.
Magpul's BEV Block, if you haven't seen one, is a combination mag-well upper assembly block / reaction rod.
It installs through the magwell but also is meant to engage the starred part of the barrel extension.
I've never used the BEV Block, but I like the idea of spreading the torque over as many surfaces as possible. The only observation I have is that the lock up in the barrel extension doesn't seem to be real positive/tight.
So... whatcha think? Reaction Rod or BEV Block?
BEV Block:
Reaction Rod: