This is probably a very simple question for most of you, but I don't know the answer and figured someone here could help.

When you rechamber a barrel, how does the pilot help guide the reamer?

For example, lets say I have a barrel chambered in 35 remington and want to rechamber to 358 winchester.......what guides the 358 reamer so that it cuts straight??? Is the pilot long enough to reach the rifling?

I know the answer is probably simple and I'd appreciate it if someone could describe the process of rechambering, step by step.

Thanks!

GonHuntin---

You'll have to do some measuring to see when the the pilot engages. You might have to use a drill in the tailstock chuck to open the old chamber up enough for the pilot to engage and then switch to a tailstop center-supported reamer.

I'm assuming you have a lathe....if not you may be out of luck.

Mr. Belk

Thanks for the answer.....I'm not a gunsmith and I don't have a lathe....my question was asked so I would have a better understanding of how barrels are rechambered......not so I could rechamber one myself.

GonHuntin---

Thanks for the clarification.....I'll try to do the same.

Most rechamber jobs are to expand the caliber to an improved version. That means the shoulder of the improved reamer will engage in the old chamber *before* the pilot is in the bore. That means the front of the reamer would be unsupported and the resulting job would look like it was rechambered with a sharp screwdriver.

I hold the reamer rigidly in the tailstock chuck until the pilot engages by half inch or so, then switch to a tailstock center and a handle on the reamer.

I LIKE to feel the reamer cutting so prefer to use a handle to hold onto if at all possible.

JB,

Appreciate your explanation too. I wondered how it was supported on a rechamber job as well.

Is it hard to get a good job rechambering if certain things aren't done just right, or is it straight forward and foolproof? Any major problems one might encounter when doing one?

If you are,for instance, rechambering a 30/06 to a 300 Win Mag that pilot isn't going to touch no matter what you do. For the first 3/4 inch or so the pilot will be unsupported.
Rechambering can be a much greater problem than cutting a new chamber for a number of reasons most of which have to do with factory quality control (or the lack thereof).
In our 30/06 to 300 scenario we have the following things to be concerned about regarding the original chamber:
1. Chamber cut eccentric to bore.
2. chamber misaligned (angular).
3. Chamber out of round.
4. Chamber chattered
5. Chamber neck oversized
6. All of the above. (I've seen it).
All of these things make it difficult to end up with a good result. Generally speaking, if you start crooked, you finish crooked. Since a gunsmith is also trying to make a living at this there is also a limit to how much time can be spent in the attempt to rechamber.
Assuming the original chamber is pretty straight, there are a couple of ways to proceed.
In the first, the barrel is set up in the 4 jaw chuck with a spider on the outboard end and the chamber dialed in. The second system sets the barrel up in the steady rest. Some like to run the steady on the threads and if they are concentric to the chamber (unlikely)this is fine. If not, a collar can be threaded on to the threads then, with the chamber supported on the tailstock center, this collar can be trued. The collar will then run in the steady.
In the actual rechambering process, after the barrel is set up, the lathe is run at around 90-120 rpm and the reamer fed into the work. The reamer may be held in one of a number of reamer holders or may be supported by the tailstock center and driven with a tap wrench, crescent wrench, or as one friend does, a pair of vise grips with brazed jaws!
Because the pilot is unsupported there is an increased possibility of starting a chatter. This is especially true if there was any chatter present in the original chamber. This is most easily avoided by not being too chicken when feeding the reamer in. If it does start to chatter there are methods to correct this before it gets out of hand.
Anyway, if it doesn't chatter, we just continue cutting (removing the reamer to clean out the chips periodically)until we have reamed to the appropriate depth as determined by our careful measurement of the action. If we have done everything right we have a 300 Mag chamber that is straight, concentric, and smooth enough that polishing is nearly unnecessary.
What if the original chamber is eccentric to the bore?
Well, in that case we have to try and get the bore running as true as possible by setting up in the 4 jaw chuck and dialing the bore ahead of the throat. This is not easily done because of the flex in the extension on the dial require to reach in 2 3/4 inches but it can be done fairly well. With the bore dialed in and running true we take a truing cut with a boring bar for the length of the body of the original cartridge. We now have a hole that is concentric with the throat area and the reamer will run true to the bore. By the time we ream past the bored portion, the pilot is engaged and the body of the reamer is also offering enough support that the neck will clean up providing the dimensions of the reamer in relation to the chamber will alow it to do so.
What if the neck of the chamber is too big to clean up? Well, then the barrel has to be set back enough to clean up the neck and throat.
If the barrel threads were eccentric to the bore they still are. Happily, this probably will not be a real problem, within reason, and the rifle will likely shoot well.
All of the flaws mentioned are quite common on factory barrels. I recently had to rechamber a 280 Remington which was custom barrelled by a pretty respected smith and it exhibited all the flaws except for chatter. In the end it was vastly improved and, in fact, looked good to the owner even with the borescope. The throat was still eccentric though by maybe a couple tenths and I could see it. (As I get older I can see less and less so my work looks better and better)
So to answer the question. Yes things can go wrong when rechambering and it isn't always straightforward. Many smiths simply run the reamer in and trust to good luck and their floating reamer holder for a good result. The good result is seldom achieved and misaligned and out of round chambers are common.
I've carried on a little too long so will shut up for now! Regards, Bill.

Bill,

Thank you for the very nice explanation.

One more question if you will?

Is the boring bar an adjustable rotating single point type cutter like used on enginge cylinder boring machine only a much smaller head? Can a boring bar be made to follow the taper of the chamber, taking an even .002" pass on the length of the body or does it just bore straight in at the same diameter to the shoulder?

Appreciate the insight.

Brent,

A boring bar can either be fixed as is used with the lathe, or rotating as is used in the mill. The compound feed table which the boring bar is attached to on the lathe, can be set at any angle and fed directly into the rotating piece by the compound tables hand wheel.

You could cut an entire chamber using only a boring bar but it would be boring (get it, boring?)...

I have done this on one of a kind experimental jobs where a reamer or series of reamers to do the job did not exist... I would recommend everyone try this once on a scrap piece of barrel so they gain a better understanding and appreciation for commercially produced chamber reamers.

Malm

Thanks GM. That is what I figured, but my only experience is with the ones used on engines and as you know they are straight, or at least should be when your done. Much more to it than just a "straight" bore of course...

Malm---

Interesting comment on chambering with a boring bar. I've done it on straight walls but always make a half reamer for bottlenecks and dies.

How do you cut the shoulder without terminal chatter and destruction??

JBELK- Could you describe the method you use to make half-Reamers? Specifically how you harden them without warpage. I've never done this myself. I've made some pretty good reloading dies using a boring bar and taper turning with the compound, but have always wanted to try the half-reamer method.-Rob

When I want to do a one off and don't feel like buying a reamer I would rather make a reamer than attempt to bore. In boring chambers for hydraulic valve cartridges it was just plain faster, easier, and better to use a formed cutter than to try and get a good result with a skinny boring bar. A set up using a pantograph arrangment was less effective than I had hoped when trying to single point a chamber. Even the cnc lathes, while they could cut a not bad looking chamber with a bar, had trouble maintaining any kind of real dimensional accuracy due to flex in the bar or accumulation of chips. With 416ss this is always a problem. It's hard to get the chip to break. I know I would probably be unable to single point an acceptable rifle chamber. I have my limits! Regards, Bill.

Jack,

R F---ing Slow...

The first one I did in 1980 on a Rem700. It was a short body, long neck cast bullet design based on the 30-30 Imp. Reground the point of the drill to remove a majority of the material in the shoulder area and then proceded cutting like peeling an onion, 1 layer at a time.

On this particular job, I cut the rim, body and shoulder and then used a seperate 30 cal neck and throater to finish. Chambering this was the easy part. Rebuilding the Remington 700 bolt head for the cartridge was a project from hell. Back then I had no idea what I was in for. Hand built a special extractor for this that was more complicated than it needed to be. If it ever breaks, I ain't home.

This gun is still in use today and is quite a shooter. I likewise have done several straight tapered chambers this way.

I have a couple of half body reamers I have made over the years for "one of" designs as well. Folks would be surprised at how well hand made, half body reamers perform. Never tried one on a die, but see where that would be most convenient.

Malm

[ 02-08-2003, 21:10: Message edited by: G.Malmborg ]

Jack,

It ain't necessarily easier, but to do it you need to set the taper attachment to the body taper and the shoulder angle to the compound. When you get to the shoulder end, crank in the compound to cut the shoulder. Like I said, it ain't easy, but can be done.

Jim

BTW, why is there more horses asses than there are horses?

Rob,

I thought Jack would have answered this by now. To make a half body reamer, start with a piece of pre heat treated tool steel of say RC50-55 and set it on centers. Next, turn it to the exact specs needed less the neck and throat and leave the pilot end oversize. Remove exactly half of the body of this reamer leaving the driving end and pilot in tact.

Using a rotary table and a mill, reduce the remaining back half of the body to that just below the lead edge of the body and shoulder to remove any possible contact with the chamber wall.

With a hard stone, define the lead cutting edge of the body and shoulder. Unless equipped to do so yourself, have the pilot ground and polished.

Try it in a scrap piece of barrel to make certain everything is fine. Cut the chamber adding the throat and neck seperately as needed.

I use this option when I get a wild hair and a wierd thought comes to mind and I don't wish to have a reamer built. I have some little nonstandard dovetail cutters I've made out of Brownells magnetic screw driver bits that work great. I have a half body tool I made for making the "turn in" dovetails for Dual Dovetail custom bases as well. There are a ton of little cutters you can make for odd jobs and for the little use these will see, they need only be harder than what they are cutting. If it wears out, make another...

Malm

Forgive the spelling errors. My folks taught me better than this.

[ 02-08-2003, 23:45: Message edited by: G.Malmborg ]

Malm- Thank you for the description. I read about this is an old gunsmithing book and have long thought about trying it. Particularily for making Lathe turned bullet molds. This was very important to me till Fritz 454 started making his custom brass bullets by CNC. I think I'll play around with making a half reamer this weekend. Thanks for the help!-Rob

Rob,

I first seen these half round reamers in P.O.Ackleys' shop years back and thought the idea and practicality for odd jobs very interesting.

Have fun,

Malm