Need advice from guys who rechamber barrels

[Black Jack]

I wanted to setback my factory bull barrel after truing my action. (Will get an aftermarket barrel but don't want to do it right now) Talking about Rem 700 in .308 After researching as much as I could wanted to do this between centers. My lathe headstock too wide. So I put this factory barrel between centers. I do not know how Remington actually chamber their barrels but if I put my indicator on the relief part right beside the shoulder I have .014" of run out. Tried it chucking the muzzle end in the chuck also and doesn't change the run out. That means that the bore/chamber is out by 14 thou from center. Is this kinda normal? Am I doing something wrong by assuming the thread and shoulder should have been cut at the same time/setup as the chamber. How can this happen? So to set it back I will have to just ream it from the center with a reamer pusher but if I have to cut the shoulder a little or the bolt nose recess, am I suppose to re dial from the shoulder relief? What is the best way to attack this problem? Tks


Ok well after taking advice of a few guys, reading and watching videos of chambering, I played with this for the rest of the month and this is what I was able to do. First I had to make a few tools since it was my first attempt and didn't want to invest in all the tools that the real gunsmith use. Also took that as a good way to test my skills to make them. I know that it was not "recommended" to do this but I wanted to do it for the experience. If I had to scrap something in the process, it was going to be cheaper to do it on a factory barrel than on a new one. So here are a few pics of the before and after of this project.

Receiver before and after. Hell they cut them with a bandsaw

Bolt before and after

Jig to indicate my action

More tools used in the process

Indicating the bore before cutting the center

Chambering

Halfway in the chambering

All back together

All in all I think it went pretty good. It was just awesome and a great learning experience. So what was done at the end was cutting the whole thread section plus about 1/8. The first attempt did not clean up enough all the way to the recess so I had to restart from scratch. There was just too much difference between bore and the thread. I wasn't happy with the result so I re-threaded the shank, rechambered and this time was deep enough to have a nice new chamber all the way out. Shot a ladder test and found a good node in the 44.9 to 45.2 of varget. Was interesting to see from a previous ladder test that the node went from a 45.5 to a 45.2. At 45.5 now my bolt was starting to stick a little. Still need to go around to find the specific load inside that node. After that, I will shoot it like this for this year and will probably install an aftermarket barrel for next year. Tks

 

[Papaneil]

Make a collar to screw onto the threaded shank butting against the shoulder. Then put barrel between centres and true the collar. Next put in steady rest. You now have your chamber running true to ream.

 

[Black Jack]

Tks Papaneil, in your experience, is it "normal" to be that much out in a factory barrel or is it because nobody does it and they only bump them on an aftermarket one?

 

[guntech]

Seldom is the outside of a barrel concentric to the bore. The barrel threads should be concentric to the chamber... should be is the wording... try and see how it works with the threads in your steady rest. Considering your question makes me wonder about your action truing. Did you "true" your action?

 

[EHG]

Have you tried indicating from the chamber and do you have an indicator with a long stem to reach into the neck and rifling to check runout there?
If the bore and chamber are not true to the threads you're wasting time setting it back. It's all in the setup. Got any pics?

 

[Black Jack]

Yes Guntech I did. Will post pictures of tools I made when I'm done with the barrel. Yes the problem is the thread not being concentric with the chamber. The sleeve Papaneil mentioned will be one way and I guess the easiest to make it work. If I put the threads in my steady rest, the chamber wobbles all over the place being .014 off from the threads. Between centers, it's the threads that bounce up and down. The center in the chuck is one I machined in place. Because of the few thousands I removed from the action face, bolt face and bolt lugs, I knew I would have to remove something somewhere from the barrel. I didn't mind that the barrel would not be concentric to the bore because I was going to remove a lick just to be able to put it in my steady rest. It's when I saw the difference between chamber and threads, just blew my mind. I indicated different spots to be sure. Inside the bold nose recess, then inside the chamber, the run out is the same everywhere. Interesting enough, at the muzzle barrel to bore is only .002 out. Tks

 

[guntech]

A few thousands removed from the action face, bolt face and bolt lugs are not truing the action...

 

[Leeper]

Remington finish reams their barrels with a through-the-bore reamer. barreled action is held in the machine, the reamer is inserted and the extended "pilot" is held in a collet at the muzzle end. The bolt is inserted behind the reamer and the machine is started. When the handle drops, the chamber is done. This was how they did it in Illion twenty years ago (man, time flies!). Don't know if they have changed now.
If I was going though all the trouble of trying to setback a barrel to fit my trued action, I would go about it this way (assuming I also had a lathe which was too big to allow me to dial in through the headstock).
First, I would figure on losing at least half the thread length and would cut that off. Then I would build a spider or cat's head or thingy -with- screws (choose the designation you prefer) and, holding the muzzle in the chuck, would mount the fixture and dial in the throat area to as close as I could get it with the fixture in the steady. I would then bore the start of the chamber to a depth of about .150 or so and to a diameter which will just clean up the full circumference in that portion. Now, I set the compound at 30 degrees and cut a bevel for the center. Now, I can either go ahead and turn and thread the tenon with the barrel in the steady or I can set it between centers to turn and thread. My preference would be to work between centers. I would leave the fixture in place since it would come into play again when it came time to chamber.
With the threads cut and fitting great, I would then set the barrel back up i9n the steady to chamber. Now; if I have set the barrel back far enough (and if the threads were that eccentric I would have set back the length of the threads) I may be far enough up in the original chamber that I can run in with my little boring bar far enough to get a pretty good, concentric, start for the reamer. So I will set my compound to match the taper of the 308 plus a bit (don't want to end up too big at the front of my cut) and cut just enough to cut all around. This will probably be possible unless the original chamber is badly eccentric (happens). If it is, I will be somewhat limited in my ability to straighten it but if it is relatively co-axial to the bore it will be possible to bore and straighten it right up.. Then I ream to depth, cut the new counter bore to give .005" clearance everywhere and there it is. That was so easy, I can't believe people charge for it.
All of this assumes two things. First assumption is that you would prefer to have concentric threads. The second assumption is that the chamber is also eccentric to the bore but, one hopes, to a much lesser extent.
There are alternative methods as well. One would involve the use of a fixture like an action truing fixture which will hold the barrel at two points. Again, one would start by cutting a true center at the breech end. Then mount the barrel between centers and adjust the fixture to be co-axial with the bore (understanding, of course, that you are only aligning the fixture with the theoretical axis since the barrel may not be straight). Now mount the fixture in the four-jaw and steady and go to work.
It is easy to see why working with a crooked barrel is much more difficult than if the barrel was straight. Every step is loaded with compromises.
Another relative simple way to work around your long headstock is to make a bushing which will slip inside the spindle and center the muzzle end of the barrel. Make this bushing or sleeve long enough to reach from the back of the spindle to the muzzle nd plus about an inch. At the end which will support the barrel, turn the sleeve to precisely the inside diameter of the spindle. Then cut a relief of about .010 from a point 1 inch from the front of the sleeve to a point 1 inch from the rear. Now split the front into four segments to make sort of a spring collet affair. This allows the tight fitting sleeve to go into the headstock spindle. The front of the sleeve is bored to fit the barrel OD. The rest of the sleeve is bored for weight reduction as much as any thing. The back end of the sleeve can be a thou or so under spindle diameter but with a short bevel to center it up. For greater precision, turn a short portion at the muzzle to be concentric with the bore. If the barrel is seriously crooked, it is probably not possible to achieve perfection but it is possible to do pretty well.

 

[Black Jack]

Updated the original thread with pics