I have a couple of apologies to make. First is to STO for taking so long to actually write up my impressions of his work. Second is to all the folks following this thread, wondering "right, but how is it *really*?"
To STO - thank you. You are a gentleman and a scholar. I'm humbled by how much work you put into this, and how much data you share. Not to mention the knowledge that you share with this community of folks.
So.
My impressions.
Out of the box (and literally out of the shipping box), my first thought was - "damn, this thing is still loud".
Then I reminded myself that I was comparing apples to bricks. I normally have my Leshiy set up with a Huma 12ft lbs reg, running at around 14-15 ft lbs. I'm originally a Brit, so 15 seems plenty, anymore an I run to my powder burners (which I'm giddy to have compared to the UK).
Upon reflection, I realize that it's *much* quieter than it was stock, so I set about resetting to my personal baseline.
My second thought on doing so was, "I must have changed the reg a bunch, as it's too quiet". Nope. Reg was the same, HS was in the same ballpark, I'm still pushing JSB 10.3's at around 830 fps. But darn, if this wasn't quiet. More than quiet, it had a nice tone. Which is, of course, completely subjective. But it just doesn't have the tinny twang or resonance that is common, just a very muted "thud".
All in all, I'm extremely happy, and if STO decides to sell these commercially, I wouldn't hesitate to recommend one. It's a significant step up from the stock core, and quieter (IMO) than running other mods on top of something like the EagleVisionCam's adaptor, or DonnyFL's adaptor. If I could bring myself to drill holes in STO's core, I think I'd have the best of both worlds - hugely quieter than stock, at the stock length, with the option to add extra suppression if I wanted.
The TL;DR summary is - STO's core is terrific, and I'm happy to have been a part of this project.