Ronvella- Thanks. Yup, I'm very aware of the barrel convergence and You must be reading my mind as thats exactly the approach I had deceided on( easiest to do on a Mill). Did you ream the chamber or bore it to the minor thread diameter? I think for a 15/16-32NS that should be .906 so a 29/32 reamer should work well. ID of the 10ga monoblock is .8460 Major thread diameter is .9375 and I'm going to counterbore the monoblock to 1.050 for a depth of.250 so that I have as much barrel steel as possible around the joint. I'll have to corespondingly step the barrel before the threaded section. The 12GaFH chamber will be about .770 at the barrel to monoblock joint which I hope will be enough of a safety margin. Monoblock and Barrel OD's are 1.116.Pressure will be kept to 26KPSI. Your thoughts-Rob