I could HEAR the spring rubbing, as much as anything. I am really happy with the King's OACP Spring kit, but still think the ISMI flat spring might ultimately be the best set-up of all.

What I know about Detonics, I've learned from reading and observing. I have one, and have handled maybe a dozen others. Storm Lake Machine makes Combat Master barrels (they used to be located in Washington, and I suspect they made some of the original barrels, too), so I can't imagine it would be easier or cheaper to make a coned barrel than to just buy one from SL. As to when Detonics switched from adding cones to making/buying barrels with a cone contour, I have no idea. My circa 1979 Combat Master has a one-piece barrel.