Bramble, The problem with your regulating device is that it adds mass to the barrels, right at the muzzles. It slows down the time of the recoil movement, ergo the bullet stays in the barrel thru a longer arc and the barrels will generally shoot across after removal. I tried exactly the same thing with my first build. It took no time at all to regulate the gun. I thought that I was as clever as hell until I soldered things up, removed the regulating device, and reshot the gun. It was then 17" apart at 60 yards. Keep the weight of your device to a bare minimum and as Allan says, you might get lucky.