Gunman,
How do you go about it?
I dont any more I retired and the tooling was sold off .
Basicaly the barels were cut off at 3&1/2" inches a centered mandrel was put in the chamber and held between centers , the back ends then clamped in a in a jig mounted on the cross slide by the lumps . The boring was done from the front/muzzel end with reamer drills and then finished to size with boring tool driven in the head stock . It was then faced off to length with a large diameter end mill .
This was a one station operation so that the facing off was true to the bores .This facing off was the key to good joints .
It scares me too.
You lads should listen to what Gunman is teaching you, a variation of the classic "line boring" method using an accurate lathe you learn in engineering shop practices. More accurate than using a vertical mill. Also he is dead on in the facing method, I even went so far as to make my own milling cutter for this work in order to get seamless fit of barrels to monobloc. Cutting the proper facing of the monobloc is the reason masters like Kirk Merrington can sleeve shotguns seamlessly without tig welding.
When you build a made for purpose jig to mount to the lathe cross slide do not use the compound, but remove it and mount the jig's adjustable base directly to the cross slide base center hole(where the compound fits). Make sure the cross slide has all excess play to the lathe ways adjusted out. I use a 2 inch hardened and ground machinist vice mounted to the cross slide (with adjustable base to the vice/cross slide interface) to hold the lumps of the monobloc securely. You will make the adjustable vice base of sufficient height to have the monobloc at center line of the headstock to tailstock when the monobloc is secured in the vice jaws. The ground and hardened vice jaws will keep from marring the surface of the monobloc lumps-but I use brass shim anyway.
I am nearly 80 years old now and I suppose you all are lads to me. Also sold my lathe, vertical and horizontal mills and tooling last year.
Bv
