Trueing action threads

J

jGEE

Guest
I often read the action threads were trued to the action center line. I think i know what that is but - what it done?

It don't seem like you could re-thread the existing threads. can someone plz explain. thanks :)
 
J Gee, take a look at this link. Action truingThat shows how I set up an action to true it. In a nutshell, I use bushings front and rear on the receiver and then run a mandrel inside those bushings. The bushings have to fit tight in the receiver and the mandrel has to fit tight in the bushings. Any slop here makes the receiver difficult to align in the truing fixture. The bushings make it easier to remove the mandrel from the center of the receiver to do the truing cuts. The mandrel is centered in the lathe to where it is running dead true on the centerline of the lathe axis. Then the receiver face is re-cut, receiver lug faces are re-cut and the internal thread at the front of the action are picked up with an internal threading tool and opened up in diameter until the threads clean up. This always results in an oversize thread from the standard size thread. Some actions clean up faster than others. It's very important to take just enough metal off at any one step to just clean up the surface that you are cutting. Too much metal removed can mean that you'll wind up having to remove the bolt handle and re-attach it to get the bolt timing correct. All truing cuts are made to the receiver in one set up which makes sure that the receiver face and lugs are perpendicular to the receiver threads. The bolt is then set up to where it runs true within about a .001" or as close as you can get to dead zero. The reason that you can't go for dead zero is that very few bolts are perfectly round especially if they have been used a lot before. The bolt lugs are then cut perpendicular to the bolt body and the bolt face is cut perpendicular to the bolt body. Don't make the mistake of removing any metal from the end of the bolt nose. The end of the bolt nose is very thin. I've seen extractors pull out the end of the bolt when the bolt nose was cut back too much. Cleaning the end of the bolt nose doesn't do anything anyway so it's best left alone.
 
Mr. Bryant thank you for your time. It is an honorable thing you experienced and not so experienced gunsmiths are willing to share your lifetime of knowledge with us newbies.

Thank you for the link, my brain won't remember everything but a "bunch" stuck!

My main confusion was truing the threads, i couldn't get that part in my mind. After you explanation i now have it. When you thread the bbl i guess the bbl threads will be a bit over size from stock/standard to match the new cut/trued threads in the action.

To me a rifle sitting in the gun rack, looks like a fairly simple machine.... How can so few parts be so complicated? What a puzzle!! joe :)
 
Yes, the barrel threads will be cut oversize. I don't open the recoil lug up and cut the barrel shank diameter larger unless it takes quite a bit more than normal to clean up the threads. I cut the barrel shank to fit the recoil lug and then go in with the threading tool until the barrel will just screw on to the action. A small flat on top of the barrel thread doesn't hurt a thing and also prevents the top of the thread bottoming in the bottom of the receiver thread.
 
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