Receiver Extension Indexing Channel and End Plate Tab (Thread damage on installation)

[Purkeypilot]

I'm curious as to the purpose of the indexing channel on the RE and the tab on the end plate after installation of a Receiver Extension. I ask because I installed a BCM Receiver Extension on a build last night and like an idiot, I didn't stabilize the tube when I torqued the lock nut (I tightened and loosened 3 times to seat the threads). After the third time, I looked at the alignment and it was a bit off to say the least, as the tube had rotated as I torqued the lock nut. I removed the whole stock assembly, and check out the threads...sure enough, as the tube turned, the tab on the end plate pretty much removed about 3-4 millimeters of the threads on the tube. I reinstalled the RE, and this time held it tight, as there were no threads to engage the tab on the end plate and prevent it from rotating as I torqued. It worked, and the stock assembly is straight now.

My question is; does it matter now that the castle nut is torqued and end plate staked? Does the indexing channel and end plate tab serve much of a purpose to keep everything straight AFTER the Receiver Extension is installed, or are they only there to aid in installation? My though process is that if the gun took a fall on the stock hard enough to twist the RE, the same thing would happen anyway (The tube would twist and the end plate tab would destroy the threads). I have another BCM RE inbound as I type this just in case. I feel like an idiot, and lesson learned for next time. Thank in advance all

[Renegade04]

Start watching at 14:56

https://www.youtube.com/watch?v=eXb_...tailpage#t=896

[Purkeypilot]

Start watching at 14:56

https://www.youtube.com/watch?v=eXb_...tailpage#t=896

It looks like he put the Receiver End Plate on backward. I'm not talking about the protrusion on the end plate that mates into the lower receiver. I'm talking about the little indexing tab that rides in the channel on the Receiver Extension that prevents it from rotating when the Castle Nut is torqued.

Receiver End Plate.jpg

[skp]

It looks like he put the Receiver End Plate on backward. I'm not talking about the protrusion on the end plate that mates into the lower receiver. I'm talking about the little indexing tab that rides in the channel on the Receiver Extension that prevents it from rotating when the Castle Nut is torqued.

Receiver End Plate.jpg

He did, it's in the comments that he realized it after shooting the video and corrected it later. I thought that was funny though.
But I don't understand what you did. How did that tab damage the threads? It should have stayed in the channel on the RE?

[Quiet-Matt]

All these things serve a purpose and work together. I wouldn't loose any sleep over the threads, but if you ever find that the RE has rotated, perhaps change it out then. Chances are that You'll never have any trouble out of it.
Next time you install one go ahead and slip the stock on and have someone apply torque in the opposite direction using the stock.

[Surf]

Sometimes you need to work with what you have and I know many people use a mag well vise block (myself included at times), but the most correct way to do the castle nut to avoid issues is to clamp the receiver extension and not the receiver via holding it down or placing it in a mag well vise block. If you do use a mag well vise block just be careful. Those who do it a lot will probably have no issues but those who are new to it have been known to create issues or break things.

[Trajan]

Yeah, when torqueing the castle nut, you want to hold onto the RE to prevent it from moving.

Not sure it really does anything once on. As you already know, there is a bit of play between the endplate and RE until tightened.

[Iraqgunz]

You can lock the tube in a vise (with copper vise jaws as an example) and then torque the nut. I also show people in the class how to use the buttstock on the tube to help hold the tube and stop it from moving.

[Renegade04]

It is amazing, of all the receiver extensions I have installed over the past 10 years, I have never had one that wanted to rotate when I was tightening the castle nut, nor did I have any issues with end plates. It is not rocket science. You either know what you are doing or you do not. If you do not, then you can screw it up.

[Iraqgunz]

I see it quite often actually. We had a few of them in my class in San Antonio the week before last.

It is amazing, of all the receiver extensions I have installed over the past 10 years, I have never had one that wanted to rotate when I was tightening the castle nut, nor did I have any issues with end plates. It is not rocket science. You either know what you are doing or you do not. If you do not, then you can screw it up.