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 Geissele Reaction Rod (et al) Vs. Magpul's Bev Block 
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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 :wink05: )

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:

Image

Reaction Rod:

Image

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Sat Dec 19, 2020 7:39 am
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I think they function the same, no? They both engage the teeth around the chamber. The rod doesn’t really have any contact with the barrel otherwise. Just like the Bev block.


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Sat Dec 19, 2020 7:55 am
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edogg wrote:
I think they function the same, no? They both engage the teeth around the chamber. The rod doesn’t really have any contact with the barrel otherwise. Just like the Bev block.


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The block has a pin to hold the upper steady. Looks like a great design by Magpul.

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Sat Dec 19, 2020 8:12 am
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BEV Block does have the lug on top to engage the upper receiver, some. Insert a bolt carrier to add more support.
The Super Reaction Rod was created to address the problem discussed, at a substantial price increase.
To me the clamshell makes more sense, along with greasing the nut and extension.

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Sat Dec 19, 2020 9:35 am
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a SUPER Reaction Rod?! ... I'd never heard of that. Looks like it has some lugs you can adjust to protrude enough to engage the edge of the ejection port in order to restrain the upper from spinning.

$175? I think I might look into drilling into that (hardened?) steel reaction rod I already own. Maybe tap the hole and add a cam that can be similarly engaged....

Image

Image

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"The said Constitution shall never be construed to authorize Congress to prevent the people of the United States who are peaceable citizens from keeping their own arms." ~ Samuel Adams

“A return to First Principles in a Republic is sometimes caused by simple virtues of a single man. His good example has such an influence that the good men strive to imitate him, and the wicked are ashamed to lead a life so contrary to his example. Before all else, be armed!” ~ Niccolo Machiavelli

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Sat Dec 19, 2020 9:57 am
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Sometime I need the clamshell and Bev block.

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Sat Dec 19, 2020 10:43 am
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I’ll also add that the Bev block needing a carrier to fully support the design is correct and additionally not all carriers fit into their receiver backwards.


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Sat Dec 19, 2020 10:55 am
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Check out the midwest industry urr. It supports the upper reciever and the barrel extension. Looks like the geissele but with a fin on top.


Sat Dec 19, 2020 11:41 am
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I have both a clam shell and the bev block

The fit of the bev block depends on the barrel. I've have some that slide right on and others that were super tight. One BCM upper was so tight I couldn't use the bev block

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Sun Dec 20, 2020 9:13 am
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jukk0u wrote:
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!

Is it safe for me to assume that this was an A2 FSB upper? Any idea what torque setting he was using?


Mon Dec 21, 2020 9:30 am
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