I like sharing this kind of stuff as it seems to generate interest and lots of commentary/discussion. In the interest of keeping things interesting around here I thought I'd share how I plumb a barrel on a receiver.
Documentation is a big deal for me. I build every rifle from a sheet that I've conjured up to record all the critical dimensions. This is nothing more than getting some numbers to work with off the action. I verify the thread pitch, measure the height from the receiver face to the bolt, barrel serial number, caliber, twist, the cartridge, etc.
Now its onto setting the barrel up in the turning center. This is the machine I use for all my barrel work. A Doosan Mecatec 10 tool slant bed CNC turning center. I've modified the machine a bit to work for barreling up actions. It's been equipped it with a Dunham 16C collet spindle nose that's able to be indicated just like a four jaw chuck. I like the idea of collets because it offers much more rigidity which means the potential for improved surface finishes. This is the "baby" of the shop.
Time to indicate the barrel and get to work! First we have to set up a special tool I made for doing this. Indicating a barrel is nothing more than getting the hole that the bullet travels down to rotate on the same imaginary center that the spindle of the machine rotates on. We want them to be concentric
with one another. I do this a little differently. Since all barrels are "bent" to some degree I decided I wanted to be able to pick the place where I make the bore concentric with the machine. I figure where the bullet is going to be introduced to the lands is the best place. So I built a tool that allows me to do this. It has different adapters for each caliber and pivots on a gimbled base that fits in my reamer holder. Here's the tool being set up for this particular caliber. My method for determining how far to stick this up the barrel is pretty "scientific". I lay the reamer next to it and mark the shaft with a black marker. It's a visual "guess" where the freebore transitions to the throat. Paring them up I mark the stylus where the scribe mark is on the reamer. Then we cram the contraption up the bore like a rectal thermometer.