When you have a barrel that has been chambered to a nonmagnum cartridge, and you later want to rechamber that barrel to a magnum cartridge, how do you get that to work.

The reason I ask is becasue in thinking about it, your magnum reamer is going to be quite a bit thicker than the nonmag chamber so you won't be able to get the pilot up into the barrel to insure concentricity. Is there such a thing as a super long pilot, or just how does one insure that its going to be worth the effort if one cannot use the pilot????

quote:

Originally posted by 22WRF:
When you have a barrel that has been chambered to a nonmagnum cartridge, and you later want to rechamber that barrel to a magnum cartridge, how do you get that to work.

The reason I ask is becasue in thinking about it, your magnum reamer is going to be quite a bit thicker than the nonmag chamber so you won't be able to get the pilot up into the barrel to insure concentricity. Is there such a thing as a super long pilot, or just how does one insure that its going to be worth the effort if one cannot use the pilot????

Easy, you dial in the bore as usual, and then with a boring bar, cut a precision hole slightly under the finished dimension and depth of the new shoulder. If properly done, the reamer will guide itself.

I didn't ask if it was easy. I asked if it was worth it. Sounds like a lot of extra work and extra cost and you still don't get the advantage of the reamer pilot entering the bore until the process is almost completed.

quote:

Originally posted by 22WRF:
I didn't ask if it was easy. I asked if it was worth it. Sounds like a lot of extra work and extra cost and you still don't get the advantage of the reamer pilot entering the bore until the process is almost completed.

I'm sorry, I should have probably used the term "simple" as in "It is a simple process".

Like I said, if everything is set up correctly, the reamer will guide itself. If a reamer can guide itself, why would you need a pilot???

WRF, your focus might be a little tight on the subject. I think what Mr. Malborg is saying it that it's no big deal, which in machinists speak means not expensive. It sounds pretty much like reaming a standard chamber into an Ackley Improved version...happens everyday. If that doesn't tickle your fancy you can whack off a couple of inches of the breech end of the barrel and start from scratch, plus you eliminate any existing throat wear in the process.

22WRF

"When you have a barrel that has been chambered to a nonmagnum cartridge, and you later want to rechamber that barrel to a magnum cartridge, how do you get that to work"

If you are compulsive, you can do what Malm suggested, or you can just run the reamer in. The reamer will center on the chamber and the new chamber will be just as concentric with the bore as the original chamber was. This is no different than using a rougher, or drill to rough out the chamber. The key is to dial in the bore. If any question about concentricity, it is quick work to take a very light cut with a boring bar.

I don't think you will find bench rest people doing this, but for sporting purposes, this is faster, less work and just as precise as cutting a whole new chamber with a piloted reamer.

Roger

Okay, then why do some people go through all of the trouble of using piloted reamers if you don't need a pilot.

Many people cut the rough chamber without a reamer at all. The barrel and reamer will need to be set up correctly. The last 1/4-1/2" of travel the pilot will engage that is when the critical cutting is done anyway. If everything is not set up correctly a 1/2" long pilot will not make things straight.

Same reason you use a reamer to cut a chamber in the first place, it is faster to set up and there is less chance of wrecking a barrel. The first chamber I saw cut was with a shop built spade reamer, it worked out fine (I would never do that).

With a floating reamer holder and a piloted reamer, close will get you a concentric bore. You don't really need pins or even a dial indicatior to get a decent bore. There is a practical difference between someone writing about and doing bench rest quality work, and the next guy trying to make a living, doing the work as quickly (read $) as is needed for a sporting rifle. This is entry level machine work.

If truth be told, more than one 7mm-08, .308, or .358 chamber has been cut with a .243 reamer and a throater. Wildcat experimenters do this all the time. When gas was still 50 cents a gallon, reamers were available only from Clymer and cost $80-100. Custom reamers took forever, if they were available at all. With relatively inexpensive reamers easily available these days from several good sources, custom reamers are the best way to go, but good chambers can be cut with anything from a boring bar on up.

Roger

quote:

Originally posted by RogerR:
If you are compulsive, you can do what Malm suggested...

Ain't nothing compulsive about it. It is quite an acceptable means to quickly and efficiently remove metal thereby saving unnecessary wear and tear to a precision reamer. And to someone who makes their living charging people for this type of work, it is good, sound practice.

quote:

I don't think you will find bench rest people doing this, but for sporting purposes, this is faster, less work and just as precise as cutting a whole new chamber with a piloted reamer. Roger

Since I also have some experience building benchrest guns, let me chime in here real quick. To those looking to have such work done, it shouldn't matter whether the gun will be used for sport or competition. The degree of care used to "perform" the job on your gun should be no different in either case.

RogerR, I don't think the smiths on this board chuck a barrel up close and use floating reamer holders and bushings. I think that they take the time to indicate properly and then do their chambering. To save time and my reamers I drill and bore with a carbide boring tool. I finish with my reamer. Check your work with a long reach indicator and check the runout of your throat and at the base .
Butch

I have to find somebody to go see this done!

22wrf,

I find it hard to believe that you, a carburizing expert and all, can't fathom this process.

I can fathom it with no problem. What I can fathom is that it will be as accurate as starting from scratch. Thats what I can't fathom.

by the way, I am no carburizing expert. But I have spoken with a couple of people who are.

They tell me that you start out with what is called cementite (or iron carbide in suspension with ferrite), and when you heat it it becomes austenite. When you quench it becomes martensite, and martensite is where you want to be (toughness and wear resistance) But you need to have adequate amounts of carbon in the steel in order to get to that martensite state. by the same token, I am told, too much carbon causes difficulty in heat treat. And finally, I have been told that one of the best ways to avoid warping is to use a gas carburization process to add carbon to the skin of the steel.

Thats about all I know about it.

Malm/Butch

I did not mean to impugn or question the practices of any member of this board. I have seen and understand the different ways of indicating a barrel to cut a chamber, and I learned to do this before sensitive dial indicators were in common use. (I paid for part of my schooling in the 60's rebarreling mausers using 2 groove 03A3 barrels purchased new by the case for $2.00 each.)

I agree totally with the need for cutting concentric chambers, and one of the reasons I still have a lathe and do this myself is that the "gunsmiths" I took projects to did not. I have witnessed the practices I described earlier in several shops.

If a shank is turned concentric with a carefully indicated bore, then held in a steady and the chamber is cleaned up with a light boring cut, a reamer will follow the old chamber quite nicely. Chambers can and are recut true without long reach indicators, using old time indicating methods. For me, it takes patience and time and it needs to be done carefully, but "it ain't rocket science".

Unfortunately, my experience is that gun owners want fast and cheap. I could NEVER make a living doing this and yes, I do consider this compulsive, in the best sense of the word.

FWIIW, I use a 10" LaBlond Regal, a four jaw and a steady. I indicate with a set of pins and I drive with a dead center. I grind my own HSS. I am slow, but I enjoy the time. My wife thinks I would be $ ahead to work a few extra hours and buy my rifles, maybe she is right.

Sorry if I raised any hair on your back, it was not intended.

Roger