Just finished putting together a new lower, which I may do a post on as well, but in this post I just want to do a quick overview on staking the end plate to retain the castle nut on the buffer tube/receiver extension. This lower uses an aircraft aluminum receiver end plate, therefore, I can easily stake it with a nail.
[1] Support the receiver extension
First & foremost, safety is your number one priority, so if your upper is attached to the lower like mine is in the picture above, be sure to clear your firearm before proceeding. Of course, you can also stake the endplate/castle nut without the upper attached to the lower.
Once cleared, remove your stock.
If you have your AR combo wrench available it would be a good idea to double check that the castle nut is tightly in place at this point in time.
Place the castle nut and the receiver end plate directly onto a block of wood. This is necessary so that when you stake the end plate/castle nut the downward force applied will directly impact this area and not place undue stress on any other parts of your firearm/lower.
[2] Nail & hammer
I used a 2-3/8" VC Sinker that I had in my tool box and a claw hammer. Besides a nail, you can also buy and use a tapered center punch to stake the end plate/castle nut. Avoid the spring loaded center punches if possible, but you can use one if it's the only thing available. Using a roll pin punch is not suitable.
Locate the spot you would like to stake the end plate (that lines up with an indent notch on the castle nut), position the nail accordingly, and give the nail a few solid bashes with your hammer. It shouldn't take more than 10 hits to displace the material and stake your castle nut.
If you are having trouble, you may have a CNC machined harden steel end plate as opposed to an aluminum end plate and using a nail is not advisable or will simply have no effect. A CNC machined steel end plate will have a very smooth side surface, whereas, most aluminum end plates will have an unfinished appearance on the sides, as pictured above. QD swivel end plates, for example, are usually CNC machined. You will have to use a tapered center punch for CNC machined harden steel end plates. A trick I use is to put down a piece of duct or electrical tape on the spot I want to stake, pressing down with my finger nail to reveal the edges & details, to give the center punch some traction on the smooth surface for the initial strike.
[3] Finished view
As you can see, definitely enough material displaced to sufficiently retain the castle nut.
A sharpie adds the finishing touch.
Final notes. It's not a question of whether "to stake or not to stake", because the castle nut has small notches specifically dedicated for displaced material from staking the end plate. So, while some may decide to forego staking or use Loctite, there really should be no excuse for not staking down the castle nut to maintain a reliable platform. And, that is exactly what you are doing, you are eliminating a possible point of failure to ensure your primary firearm is always ready. Whereas, by not securing the castle nut you are allowing various scenarios to possibly unfold. Consider what would happen while if you were firing the weapon or even while in transit, the takedown pin spring being retained beneath the end plate could easily be lost if that section were to loosen up & come apart. Now you have an AR-club (still illegal in CA) in your hands that could separate (lower from upper) at any given second. You could MacGruber it and put some duct tape over the retaining pin cap (if spring is lost) to hold it in place, but would you really want that? Of course not. Additionally, consider if you were firing the weapon and, as the BCG was moving back, the takedown pin comes loose, thus allowing the upper to separate from the lower. Not a good situation, basically a catastrophic failure that would render the weapon useless, nevermind the BCG implanting itself into your forehead or being ejected 15 ft away from you. A ridiculous scenario, maybe, a possibility, yes, an avoidable scenario, definitely.
As stated previously, if you are having trouble using a nail to stake your castle nut, you may have a CNC machined harden steel end plate as opposed to an aluminum end plate. The CNC end plate will usually have a very smooth machined side surface. A tapered center punch will do the job.
Lastly, if you were ever to decide that you needed to remove your buffer tube, say to install a Magpul UBR, it is easy to unstake the castle nut with the right tools, a roll pin punch and a Dremel tool.
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