So I've finished my first AR build, but when I went to fire it my stock wouldn't stay in position. Every time I would fire with it extended to where it was comfortable for me it would collapse in on itself.
I have 2 guesses for what is causing that, my first guess is that it was a used stock and maybe the locking mechanism is broken.
My second guess is that its a daniel defense buttstock on an aero buffer tube, maybe they aren't perfectly compatible?
I have since ordered a new daniel defense stock (I had planned to anyway because I had wanted to do a multicolored theme originally but I decided I didn't like it once it was built) and now im wondering if I need to replace the buffer tube as well? I'd have ordered one from DD at the same time if it was in stock but of course, its not.
Am I correct in assuming what the problem is? Or is there another problem that im not seeing?
I appreciate any help given

See if you can adjust the locking pin length. Most can be adjusted after using a punch on the roll pin.

This.