I got the ACP under shot bolt today. Now I have never handled the Cooper-T better bolt for the VM-68, but I did have a Cooper-T better bolt for the sniper. If the Cooper-T VM-68 bolt is similar to the Cooper-T sniper bolt, then the ACP design is furthest from.
Like I said I just got it in the mail and it will be awhile before I get a chance to shoot it. My backyard is small. No really small. So maybe proof (or lack of) is in actually using it. The bolt design isn't anything like Cooper-T's design. Chauncey's design used a bottom cut channel that ran the length from the port exhaust to the front of the bolt. So all the gas is channeled to the bottom of the ball. Hence a reduction of FPS as the flow is channeled specifically at the bootom of the bolt. The ACP took their standard open faced bolt, cut to oring grooves around the valve port, and then removed 1/5 of the bottom section of the open face. It's basically an opened faced bolt with a wide cut down the bottom center.
Think of the letter 'C' and that's the face of it. The only thing I can think of for the reason for this design is it still has the bolt velocity screw inside of it. But in a backspin application there are other ways to limit flow on the VM.
This might have been poorly researched on their part. And what's sad is this bolt is well machined. The face is nicely rounded to cup the ball, the port is angled for flow simular to AKA and Mad designed in high flow and zero flash. It's a quality piece in the hand. But I wonder if they actually tried this out?
I already have a ACP open faced delrin bolt and love it And my experience with other backspin bolts tells me this isn't going to give me the results I expect. But I'll still have to give it a try. I might fill this one with epoxy and cut a channel like Chauncey's original design if things aren't working as expected. Or design a plug insert for the bolt.
Who knows maybe I'll eat crow once I run it through some. But experience with this tells me otherwise.