This resembles to my own carnage with tang inlet a year ago. That´s OK , Stone River. If you´re tech type guy, you´re just looking for all details you can imagine (very well) and since being new to this job, simply not able to distinguish the importance ratio between them during the job or better, in advance. Confusing for a tech mind
Together, I spent about 5 whole days on tang (ok, it was whole-wrist lenght hook-breech type...) After about two hours of work, one is incapable to see the trees for the forest around :-)
Make the gap at the rear of the tang a little (but for sure) wider than the one between breech and breech-face of the wrist curently is. You´re going to put the barrel in and out many times, tap it and other parts in and out maybe even more times-it will all settle down, some gaps will close a bit, some might emerge (but if no mistake is done, they should just close). Also before drilling breech and tang bolts, you´re going to put the barrel in and whack the gun against the floor (buttplate on, pile of rags under!) several times, then clamping it to get no shear load on the bolts after driling tight holes.
So just before preparing for surface finish, check again the breech and tang gaps. Then take care about it-glue two or three layers of printer paper to back end of barrel chanel or whatever you feel comfortable with (count some little excess for compresion during shooting). One or two paper thickness is no deal in vent placement. Now, when the barrel has a lot of time to "sit down" better, it´s just unnecesary work and worries in my opinion.
Just remember-you definitely want a hair gap behind the tand even after the finish is done and the gun is assembled. It might close after first shots if there´s some room for movement, or might rest as is-then a drop of wax or putty made of caoline and linseed oil is pressed in to seal. You want this to let the barrel push against big area of breech face, not against small area at tang end-this ends up with cracked wrist.
Good luck
