A brake will be in order here. I just got back from shooting this new stock, on my old beater .300 Winchester Mag. Mind you, it's my beater gun and I've long since borrowed the brand new 6-18x Leupold to a more deserving gun. I figured to get remotely close to a heavier .338 Edge I'd need the lightest gun I could get my hands on. The plus side, is without a scope this gun is light. ~7 lbs. The downside is i didn't get a chance to test eye relief, since there wasn't a scope. (based on today's experience, probably not an issue anyway. 1.5" travel. I figure one's shoulder to move almost as much on a non-recoil suppressed rifle)
That said, I chambered a 208gr A-Max, same handload I use in my Sendero. Roughly 2800fps from a 26" barrel. I touch my cheek to the stock, basically sight down the barrel, (mind you, I'm expecting a gyration of pitch i.e. muzzle rise and fall) and the gun recoils straight back, and straight forward in a relatively smooth motion and is surprisingly controllable. Remember when I pushed my cheek into the comb? I about got my face pulled off by the Overmolded rubber comb that first grabbed my skin, then my cheekbone and accelerated it backwards, (i'm no physicist but F=MA!!) total movement, about 1.5".
Which brings me to my conclusion. The mystery of WHY it works is over. The big ugly plastic thing on the end is nothing more than the other end of a spring loaded mechanism that travels parallel to the axis of the comb of the stock. Nothing fancy, just back roughly 1.5" and forward 1.5". With the gun shouldered i can move the mechanism with my hands against my shoulder.
When i used to shoot this gun with a factory stock (with hard factory remington recoil pad), after ~20 rounds i'd develop a strawberry and a flinch. My calculated shoulder tells me that recoil from this gun is slightly stronger than my .22-250. probably somewhere in the .243 range. There was very minimal muzzle rise, which I instantly noticed. Once the stock extended back to it's original location before the shot, i was back on target (more-so than how it would be with a normal lightweight .300 Win Mag. anyhow, due to the near-complete lack of muzzle rise.)
In retrospect, I won't be using this stock. for someone willing to trade not putting their face on the stock to sight down the gun, it would be a great buy. Resting my cheekbone on the comb is something i've always done, and consider necessary to any accuracy minded shooter of any discipline. Take this for what it's worth, just because it isn't for me doesn't mean it doesn't have an application somewhere.I'm sure someone recoil sensitive for a medical reason would benefit from it though, no joke, it felt something like a small varmint rifle. Does it work for what they said it would? yes.
I know where there's a nearly untouched Compstock for sale if anybody needs one.
