Very quick range impressions. Approx 180 rounds through.
The good: Rifle functioned well as far as cycling and firing was concerned. Very controllable, quick to point. Recoil no more than a standard AR15. I did a rapid dump of 3 lar mags and 2 pmags back to back with no functional issues aside from a bolt hold open issue.
The bad: Bolt hold open is sketchy for me. I even trimmed 3/4 of the rubber bumper off the back of the buffer, but it still just barely catches. I would say bolt catches about 25% of the time. It is a functional annoyance if you are not counting rounds down range (which I usually do). Also a bit of a #### block if you are doing fast reloads. I'm reticent to trim the buffer more because it must be impacting at the back of the buffer tube.
I was wearing a thin sweater, and later a t-shirt as the day got warm and the stock beat my shoulder up something fierce even with a very firm pull into the shoulder. Maybe a tac vest is in order, or a custom but pad. The shoulder rest is somewhat small and the pattern machined into it gives it some sharp edges.
The WTF: Twice the charging handle tapped me in the upper lip even with the stock fully extended. I do tend to hunker down on my rifles, so I may have to modify that approach. It does make me question the viability of me personally firing the gun in a less than fully extended position. This may be an issue inherent with trying to put a rifle into a subgun length.
Overall TL

R: As a civi, it's just a "wow neat stock" piece. Looks great and functions good, but there is no real advantage of having this stock over a telescoping M4 style stock, and it actually carries some negatives (for me) over the traditional options.
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