I have read many threads on this forum where people have mentioned that they have trued up the threads in their action before putting on a new barrel. And I have always kind of wondered about that because I wondered what would be the benefit of having the threads trued up if the bolt itself was not perfectly concentric to the threads.(I hope I am saying that correctly)

Now I read an intersting article in Rifle Shooter magazine that tells of David Miller's actual method of truing on the raceway itself, removing the factory threads, and then cutting new threads.

I have never really studied these actions enough to know how much metal has to be left in the front ring for the action to be safe, but what I am wondering is whether anyone else besides David Miller uses this method of truing on the raceway, and if so, what is all involved in it.

Blue

blue, I suspect that there was some editing and pruning in the wrong place in the article you read. If David Miller meant the cylindrical or bolt bore part of the receiver it would make more sense. It isn't normally necessary to remove the old thread. You previously have aligned the receiver bolt bore so that bridge and ring
are both on the rotating center of the machine, pick up the old thread with a properly shaped tool for the thread and take light cuts to at first remove the eccentric, tapered or skewed( threaded on an angle to the bolt bore) part of the thread section, continue increasing the diameter of the thread until it cleans up plus a few more thousandths to insure uniformity and that's all there is. Often the ammount is only .015" or .020 larger than the original diameter. If the original thread section was skewed, though only .005" at its worst off center, this could mean that you could never zero a scope for lack of adjustment, and or weird forend bedding into the bargain. If the thread is eccentric to bolt, then after firing the bolt could be hard to open because the shroud on the bolt head could be eccentric to the case as fired, whereupon the shroud would bind on the case rim during turning out of battery. Not a plus on a hunting rifle or a target rifle for match shooting. There are instances where the barrel fitter might take the receiver threads out to larger diameter. When there is concern that the wall thickness over the chamber leaves too much to chance or the receiver has all the threads removed as a continuation of the claw extractor clearance, the fitter might in the interests of caution increase thread diameter to where he has a full thread in the receiver and a matching increase in barrel thread diameter.

To those who might ponder why I called the ctg. rim surround of the bolt head a shroud- 'cause that's the job it does. It covers the dead hull of a once live cartridge.
seems to me to be a better title for the job description than to call a bolt sleeve a shroud. The sleeve can have a
lot of other jobs to do than to just cover the fanny of a bolt. What other one word could be used to describe the cartridge rim surround/support of a firearm bolt head?

foreskin?

System98



I quote from the article



"The term blueprinting"merely means that are surfaces are trued and concentric with the bore. Most gunsmiths true on the barrel threads, and that usually works well. However, David Miller goes one step further. He ahd his colleague Curt Crum true on the raceway, remove the factory threads, and cut new ones to ensure concentricity. they surface grind the action with the exception of the front surface of the recoil lug and the front of the action ring. These two items are trued on a machine lathe after the barrel threads are recut"



Blue

Rojelio, Words for things or happenings are very often provided by astute observers by way of personal experience. Hampered by a parental decison made for me in my very early life I can not judge the aptness of your word selection nor to inquire what occasioned it.

Perhaps the most eloquent response to a decidedly sophmoric post that I have ever seen. So well composed that it sounds almost Churchillian...Now to clean up the coffee I just spilled on the keyboard..gotta stop laffin' first though!

http://www.gtrtooling.com/prod07.htm

Blue,
In usual practice the threads are trued to be in line and concentric with the bore of the receiver. This work is both straightforward and complex. Straight forward because the goal is easily seen. Complex because it is not always easily reached.
In most cases involving anything other than dedicated BR actions, there is some warpage of the receiver in the heat treating process. This means the bore may not be straight. When a mandrel is shoved through this action both the mandrel and the receiver will deflect to a certain extent. Setting up the action so the mandrel runs true may not result in truly straight and concentric threads in this instance. In fact it would be more accurate to say it won't.
In most instances the threads are close enough that recutting them will have little benefit in the instance of a hunting rifle. I have seen some actions which were grotesque in this regard though and they certainly benefitted from the truing operation.
The methods for setting up and truing actions and threads have been refined over the years and every accuracy minded 'smith has his pet technique. Often the technique is less important than the dedication of the guy doing the work. The best technique in the world can still produce a poor result if the praticioner is inept!
I do know there is more than a little BS involved in some of the descriptions of truing operations carried out by some. I also know that the best "action specialists" do a remarkable job of making chicken soup from chicken droppings in many cases. Regards, Bill.