Cleaning up existing chambers

[bigngreen]

It's not uncommon to want to set back a chamber a thread to give your chamber a new surface finish, if you need to completely correct a chamber it's dependent on case taper mostly cause you have to go easy and clean a LOT to keep from rolling a chip then you have to go just past first full contact to full reamer support to bring that reamer into full contact and cut to get the finish chamber. Personally I'll only do this if the barrel needs to be retained for a specific reason and I charge MORE than chambering a new barrel.

 

[Mram10us]

It's not uncommon to want to set back a chamber a thread to give your chamber a new surface finish, if you need to completely correct a chamber it's dependent on case taper mostly cause you have to go easy and clean a LOT to keep from rolling a chip then you have to go just past first full contact to full reamer support to bring that reamer into full contact and cut to get the finish chamber. Personally I'll only do this if the barrel needs to be retained for a specific reason and I charge MORE than chambering a new barrel.

sounds good. I misunderstood JEs reason for doing this. Thought it was to correct dimensional flaws not just give the chamber a better finish, which that one definitely needed.

For off center chambers (still not sure how that can happen with a piloted reamer) it seems you have to take the neck length of the chamber and correct that much as a minimum.

 

[tobnpr]

For off center chambers (still not sure how that can happen with a piloted reamer) it seems you have to take the neck length of the chamber and correct that much as a minimum.

Ya know, I've struggled with this as well.
While I've personally never seen one "that bad", pics don't lie and I've seen them where the freebore ends and it looks like the reamer had to have been in at ten degree angle...

Can't happen with a pilot that has clearance of a few tenths.

 

[Mram10us]

Ya know, I've struggled with this as well.
While I've personally never seen one "that bad", pics don't lie and I've seen them where the freebore ends and it looks like the reamer had to have been in at ten degree angle...

Can't happen with a pilot that has clearance of a few tenths.

I wonder how they are able to flex a hss or carbide reamer without breaking .... my guess is the pilot was waaaay to small??? Again, just thinking out loud

 

[25WSM]

Obviously it's not to hard to cut a crooked chamber. I've never seen a reamer that didn't have a pilot either fixed or removable. So it seams that the pilot does not prevent a crooked chamber but I'm sure it helps. I think the way the factories chamber is why they are not straight. I was at a very large rifle factory and saw how they chambered and I was blown away. There was a container of barrels that had threaded shanks and no chamber. A barrel was put in a collet and then the tailstock had a turret with 3 reamers on it. They had lube run through them. Each reamer took about 15 seconds. So they were doing a chamber in under a minute. I couldn't believe it. I didn't see them crown them but I heard that TC does crowns on a drill press.. So basically if you don't dial in the bore during setup and then you cram the reamer in fast as you can you are not going to have straight Chambers. I mean look how thin the steel is under the removable pilot I'm sure it doesn't take much to flex that area. The rest of the reamer is very stiff in relation to the pilot area. A solid pilot would be much more stiff. But you have to admit that most factory guns shoot quite good considering how fast they are produced.
Shep

 

[Mram10us]

Obviously it's not to hard to cut a crooked chamber. I've never seen a reamer that didn't have a pilot either fixed or removable. So it seams that the pilot does not prevent a crooked chamber but I'm sure it helps. I think the way the factories chamber is why they are not straight. I was at a very large rifle factory and saw how they chambered and I was blown away. There was a container of barrels that had threaded shanks and no chamber. A barrel was put in a collet and then the tailstock had a turret with 3 reamers on it. They had lube run through them. Each reamer took about 15 seconds. So they were doing a chamber in under a minute. I couldn't believe it. I didn't see them crown them but I heard that TC does crowns on a drill press.. So basically if you don't dial in the bore during setup and then you cram the reamer in fast as you can you are not going to have straight Chambers. I mean look how thin the steel is under the removable pilot I'm sure it doesn't take much to flex that area. The rest of the reamer is very stiff in relation to the pilot area. A solid pilot would be much more stiff. But you have to admit that most factory guns shoot quite good considering how fast they are produced.
Shep

I don't see how a piloted reamer can do anything other than follow the bore or break. Slight oval chamber makes sense if pilot isn't tight, but an off center chamber??? I'll ask the machinists I know and see if they can spell it out for me.
btw, glad you're back and hope you're feeling better

 

[25WSM]

I'm getting there. Thanks
Shep

 

[25WSM]

I'm thinking of opening my shop back up. I've been retired too long. I kinds sucks being retired.
Shep

 

[J E Custom]

So glad I'm not a gunsmith....
I'm not grasping how cleaning up a chamber with only .062" (1 thread) of cleanup can fix much. Lets say a 300wm is our rifle to fix. The rear of the chamber will be .5136". Let's say the worst wall is off by .003". That is .006" in circumference difference. The thread worth of correction puts us at .0068", which is just enough to fix it.
Just thinking out loud, but why not 2 threads worth? That gives over .013" worth of correction for a chamber and on most tenons, the same number of threads actually touching the reciever threads. Again, just spit balling here.

We don't go for a full thread of chamber cut, (.0625) only what it takes to get a concentric chamber and fresh throat and lead angles. When this state is reached, at what ever the dimension we then remove the same amount from the barrel shoulder, barrel thread tenon, bolt recess. depending on the required head space counting the thickness of the new precision ground recoil lug.

The normal limit as to how much threads you can remove safely is .0625. any more than that is not recommended for several reasons. Two of those are the recoil lug seat will be to little if at all and the lug may/can be off center and the strength rating for the thread design is diminished by 1/16th% and also the safety factor of the design requirements.

There is no reason to remove any more chamber than necessary. My personal limit is one thread.
Sometimes, if the cartridge is diminutive we may decide that 1.5 threads will be ok as long as it doesn't effect other requirements and bolt loading is low. Many times we will change the design of the chamber(Different cartridge or even AI) and have to change the barrel ID so if we can clean the chamber and lead with 270o (.0468) we can roll the old barrel ID around where it ends up under the stock and then we can place a/the new barrel ID (The new chamber cartridge designation on the barrel in the proper location where it belongs to prevent shooting the wrong cartridge.

J E CUSTOM

 

[J E Custom]

I don't see how a piloted reamer can do anything other than follow the bore or break. Slight oval chamber makes sense if pilot isn't tight, but an off center chamber??? I'll ask the machinists I know and see if they can spell it out for me.
btw, glad you're back and hope you're feeling better

The pilot does follow the bore, but the back of the reamer will follow the holder or the chuck.

normally the pilot can mar the bore when this happens because it can flex a few 10ths but the cutting part of the reamer will follow the angle of the reamer holder or chuck on a CNC machine because it is much stronger.

J E CUSTOM

 

[Mram10us]

The pilot does follow the bore, but the back of the reamer will follow the holder or the chuck.

normally the pilot can mar the bore when this happens because it can flex a few 10ths but the cutting part of the reamer will follow the angle of the reamer holder or chuck on a CNC machine because it is much stronger.

J E CUSTOM

Exactly what I said above. You can get a chamber that is maybe oval, but how can a piloted reamer cut a chamber that is off center from the bore?

 

[Edd]

If a cartridge has .012" per inch of taper, a .062" difference in length makes .00075" difference in diameter.

 

[Mram10us]

We don't go for a full thread of chamber cut, (.0625) only what it takes to get a concentric chamber and fresh throat and lead angles. When this state is reached, at what ever the dimension we then remove the same amount from the barrel shoulder, barrel thread tenon, bolt recess. depending on the required head space counting the thickness of the new precision ground recoil lug.

The normal limit as to how much threads you can remove safely is .0625. any more than that is not recommended for several reasons. Two of those are the recoil lug seat will be to little if at all and the lug may/can be off center and the strength rating for the thread design is diminished by 1/16th% and also the safety factor of the design requirements.

There is no reason to remove any more chamber than necessary. My personal limit is one thread.
Sometimes, if the cartridge is diminutive we may decide that 1.5 threads will be ok as long as it doesn't effect other requirements and bolt loading is low. Many times we will change the design of the chamber(Different cartridge or even AI) and have to change the barrel ID so if we can clean the chamber and lead with 270o (.0468) we can roll the old barrel ID around where it ends up under the stock and then we can place a/the new barrel ID (The new chamber cartridge designation on the barrel in the proper location where it belongs to prevent shooting the wrong cartridge.

J E CUSTOM

I am curious why rem 700s have a lot of threads, but thompson center compass have around 6 threads, same diameter and tpi. As for normal limit, I'm wondering why we wouldn't chase the threads since there is room for a couple and the recoil lug seat just needs enough to center, even though some guys thread all the way to the shoulder.
Agree, there is no reason to remove any more chamber than needed.

 

[shortgrass]

I don't know why any gunsmith would bother to try a re-chamber on a factory (Win., Rem., Howa, Savage, etc) barrel. It's just not worth the time or effort involved. Just cleaning one up, to make certain no carbon remains, can take a fair amount of time. Running a chambering reamer into a barrel that has some carbon deposits can dull the reamer. Rem. , Win., Howa barrels are hammer forged. The chamber is "roughed-in" as part of the hammer forging process. That's how you get a chamber that's 'crooked' (and a barrel that's crooked, too). A good custom barrel may be a good candidate for re-chambering. Each will have to make their own determination as to whether it's worth while, or not.