In this discussion Scearcy asked for more detail on my shop made seating tool. Credit goes to my father as this was part of the inheritance. He mainly used it to push fixed ammo with oversize or long bullets into the chamber for his match shooting.
For my use as a breech seating tool first I took two decapped cases that have been fired in my rifle. In case one, on left in picture, I belled the mouth with an expander so that it would just go into the chamber. I cut two brass rods so that the bullet would drop in the case for starting into the breech. My thought was to push it in in short steps. I found this not necessary, although with harder bullets it might be. FWIW I'm using WW cast bullets. Case number 2, on right has a brass rod that is threaded on one end and the case is as well. this should make for uniform depth. My target is .080" past the case mouth. If this works I'll experiment with the final depth to see if I can dial in accuracy.
Next picture is the tool and cases together.
Close up of the top:
Finally how the tool fits in the action:
Note the action is one waiting for building with just a barrel stub screwed in. You might notice the safety is not standard. One of the first things I father changed on every No.1 he owned was to modify the safety so that it rides in a milled slot on the tang. With a button more streamlined than the factory bump.
As I mentioned in the other thread, it appears that a 1903-a3 bolt is nearly the same diameter as the round body. The rear locking lug also looks to be the right size for one side. If you had a surplus one that might be a good place to start. However if you have access to a lathe and mill it likely would be less trouble to start with steel and mill each part. This one has several visible seams where my dad silver soldered it together. the golden part is what I had to replace and sourced a cut out from a circ sawblade that was otherwise junk. There it is. Let me know if you wish for more pics.