When installing a receiver extension tube, what is the best method to ensure good alignment of the stock? In other words, how do I avoid ending up with the stock canted when it is eventually installed? Search-fu here and elsewhere generates various videos/articles saying to align the tube before torquing the castle nut but little detail on how to do this. Is this done by eyeball, or is there an indicator of some sort that I’m missing? Am I obsessing over minutiae?
Yes - the notch on the castle nut and the divit that fits into the receiver - check it out and you’ll see.
I eyeball it. If after you torque the castle nut, the tube is rotated, loosen and try again. Stake the endplate when you’re happy with results.
I’ve never had to manally index a Receiver Extension. 
The plate only goes onto the lower one way… and there’s a tab in the plate forces the RE to be centered up. I suppose there could be some slight play in the equation, but not enough to be noticeable.
OK, got it. The index tab on the end plate should have been obvious now that I look at it again. Just another Homer Simpson moment on my part. Thanks for the replies.
The receiver extensions I have installed all rotate about 5 degrees and I try to end up with it installed straight.
Shouldn’t be doing that, as others have said it only goes together one way (straight).
My least favourite tasks in lower assembly are, in order of most hated, to slightly less hated:
- Front pivot pin install
- Carbine receiver extension
- Bolt catch roll-pin
I think my hatred isn’t necessarily the installation of the carbine RE, as much as being spoiled rotten by doing too many rifle builds.
The Bolt catch roll pin sucks for sure. But the Trigger guard roll pin is more nerve racking.
I’ve never broken a tab off… and I know how to support it properly… but it’s still the hump in the lower assembly for me.
I don’t know what else to say except the clearances between the interfaces of the endplate to the lower receiver and the clearance between the receiver extension and the endplate add up to cause a minor amount of play. Not a big deal and is obviously eliminated when the castle nut is torqued.
I, too, haven’t broken off any ears, but…
You’re right; the bolt catch pin causes me to belch obscenities, the trigger guard pin causes me to get nervous.
My new trick for getting the front pivot pin/detent in, is using angled pliers to grip the detent/depress the spring, and gently using the pin itself to retain the detent until I can pop it into position. I tried it Sunday on a build for my old man, and it worked really well, after countless f-bombs, and crawling around the garage. I’ve tried using a punch to hold it back, I’ve tried tape, I’ve tried using box-cutter blades, but the pivot pin itself seemed to be my new favourite.
That being said, I need to see if Grant will sell me a bulk pack of springs and detents. I am totally over that easter egg shit.
I just did my seventh stripped lower this Sunday, and I swear to God, I don’t know what my malfunction is, but I can NOT, for the life of me, ever remember how to set up the springs for the trigger and hammer without looking it up. :suicide2:
I put the stock on the receiver extension, place the pistol grip and the lower rear part of the stock in a vice and gently tighten until centered/snug then stake. Lower sits up at a 45 degree angle.
I used to use the pivot itself until I bought one of these:
http://www.brownells.com/.aspx/pid=26488/Product/PIVOT_PIN_DETENT_INSTALLATION_TOOL
Chad, thank you, Sir!
While using the pivot pin as a retaining tool itself was the best method I’ve tried, I’m over the drama with the springs.
I will gladly drop $16 to not have to crawl around with a flashlight every time I get to that step of the assembly.
This past weekend I know an hour of my life was spent over one measly spring. Turned out it had ricocheted off my light ballast, and was sitting under my bench vice the entire time. :rolleyes:
Thanks again for the link, brother-man!
Just realize that while this is a great device, you need to be careful pushing the pivot in behind this tool. If not careful, the spring can still launch the detent. (Just a lot less often)
This makes a lot to sense. I have yet to install a receiver extension and endplate that didn’t have a little play. This is with quality parts from BCM and Noveske mostly. I have one of the “multi-tool” AR wrenches that has the 3 prongs for the barrel nut, flash hider slot, and a smaller slot that fits the “rail” on the bottom of the receiver extension. I just hold the RE where I want it (completely vertical) and tighten the castle nut with the wrench in my other hand. Seems to work out pretty well.
You can alleviate that even more by making your own for dirt cheap to free.
When you turn this type 90 degrees after pushing the detent pin through with a punch you end up with a little shelf to lay the end of the pivot pin on, so it can be positioned directly over the detent pin right off the bat as opposed to trying to bridge a gap before the pivot pin can get over the detent pin.
Hole position from the shoulder can be fudged to suit taste, as long as the hole is at 90 degrees to the shelf.
Cold rolled steel is a bit harder overall and has a smoother finish than hot rolled along with slightly better dimensional quality.
Back to canted receiver extensions. If you are reusing an old extension, the groove in the 6 o’clock position can be damaged from previous installation. The groove is only cut through the threads and previous torquing can widen it where the endplate tab fits once installed.
Before torquing the endplate, snug it up, put in a 30 round mag, A2 style grip and stock. This will give you 3 points of alinment to check. I fit my stocks slightly canted 5 degree clockwise because the majority of my shooting is right handed.