I am no military armorer, but I have not seen or heard of a buffer tube backing out or otherwise being a problem due to not having a staked castle nut. But please tell me if I am wrong. It seems staking the castle nut is unnecessary.
I’ve fixed at least 75 lose ones that were never staked (civilian guns).
The proper way to do it is to stake after torquing.
Another way is blue loc-tite but they’re a bitch to disassemble if you ever need too.
Yes it is very necessary to stake the castle nut. I have seen two receiver extensions come loose in the same range session. If you plan on using your rifle for more than a couple of boxes of ammo a year, you better stake the castle nut.
to be brief,
once upon a time, AR technical knowledge was passed on from person to person… we didn’t have internet databases nor national links to people with accumulated knowledge, and a vehicle for vetting experiences and opinions. staking was something COLT did at the factory, and was Voodoo- the individual or “custom” builder rarely did.
and it was part of the basic daily function check to inspect your index mark on your castle nut for movement, and you never went anywhere without your handy dandy spanner wrench.
tell you anything? 
thank God for progress.
Absolutely necessary. I have seen many of them work loose. Whether or not someone is smart enough to heed the advice is something totally different.
Stake
In my limited experience of about 25 guns I have had three come loose.
The receiver extension tube on my “Frankenrifle” AR15 came loose twice so I staked the castle nut…no probs after that.
YES. Stake it.
I used to think having the nut tightened good was sufficient, but sure enough I had one come loose not to long ago. Stake it.
And another vote… STAKE IT.
stake it
From first hand experience, stake it… and for Pete’s sake… ad easy as it is, why wouldn’t you?
No don’t stake it. Then you will learn through your own that it needs to be staked.
I saw one loosen on a stock Bushmaster. Things went down hill fast. The guy that had the Bushy didn’t have a clue what was going on and all of a sudden his stock was turned around, basically butter-side-down. Of course on the inside of the buffer tube, the buffer retaining pin and spring were now where the buffer, spring, and BCG should only be- in the buffer tube. Still not knowing what was happening, he though he should clear his rifle, which was good thinking- except that when he got the bcg about halfway back into the buffer tube, it seized up with a buffer retaining pin and spring wedged under it. There was no going back, no going forward from that point on. And the BCG was half in the buffer tube/half in the upper, so popping the pins and dissassembling the rifle was also a no-go. I ended up just taking the buffer tube all the way off for him(he had no idea how to do it), and getting the parts out that way. In the meantime, he had lost his rear takedown pin-spring, and had no idea. So yeah, I’d stake it.
Stake it. During several PRG classes I have taught, unstaked castle nuts have come loose. A spring-loaded center punch will cost you about $15. Do it.
Stake it .
Or not . Up to you.
Why worry about something you could fix in 90 seconds with a hammer and nail? If it caused me any lost sleep I would consider myself lazy.
True. That’s what I did. Lowes sells one that costs just under $10.00
Second this motion.
had the same thing happen to me after I changed out a stock and figure I would just tighten it god to see f I liked it.
Well…never did stake it, and it loosened a little causing catastrophic failure as you described. I got to sit on the bench and fix my gun while everyone else continued with the class I paid 600.00 t attend. I then had to beg for parts that luckily someone had.
it all worked out, but lesson learned.