Fitting and Chambering a Custom Barrel—Part 1

By Joe Fischnaller
Owner – Moses Lake Custom Rifles
GCA SilverPLUS Member

Introduction

About a year ago, in an article I wrote for GunTech, I discussed my method of blueprinting a Remington 700 action to wring the greatest possible accuracy from it. We made a number of cuts on both the action itself and the bolt; each time removing as little metal as possible, but enough to assure the bolt and action were as true as possible in all areas that matter for accuracy.

Now that we have our perfectly blueprinted Remington 700 action, we will need to add a barrel and free float the resulting barreled action into a good quality stock. In this article, I would like to discuss how I fit a custom barrel to a Remington 700 action, again, for the greatest possible accuracy. There are certainly other methods to accomplish this task, but this is the way I do it, and it does result in a very accurate rifle. In this instance, we will be building a .20 VarTarg, using one of Dan Lilja’s great barrels

Inspecting the Barrel

Even though a new, custom barrel should have no faults; that is not always the case. Just last month I received a barrel from an excellent barrel maker, one of the best, and found several imperfections in the bore.

It always makes good sense to carefully inspect the barrel before you begin work on it. There are two procedures that need to be performed before work begins.

The first thing I do is to slug the barrel. Soft lead slugs can be purchased in any caliber from Brownells, and other sources as well. The procedure is performed by starting the lubricated slug into a lubricated bore and then slowly pushing it through the length of the bore from breech end to muzzle with a wood dowel of appropriate size. While moving the slug through the bore, carefully feel for any areas where the bore is tighter or looser. You want the slug to move smoothly through the bore with no loose or tight spots.

The second step may not be available to you, since it requires a bore scope. A Hawkeye Bore Scope is a tool you should consider purchasing. They are fairly expensive but worth every cent. I use mine almost every day. If you have a bore scope, use it to carefully inspect the full length of the bore.

Hawkeye 17” Slim borescope kit

Assuming these procedures produce satisfactory results, you may be confident you have an excellent barrel blank that, when properly fitted to your properly blueprinted action, should produce a very accurate barreled action.

The Tools You Need

Certainly, you will need a good quality lathe with a four-jaw chuck, and with a properly constructed spider at the outboard end of the spindle. A spider is nothing more than four drilled and tapped holes in the outboard end of the spindle. These holes should be placed so they each line up exactly with the center of each of the jaws on your four-jaw chuck. This will allow you to precisely center the muzzle end of the bore within the spindle bore of your lathe.

In addition, you will need a good quality one inch micrometer or at least a high quality set of calipers. I would prefer a good micrometer, as they will be a little more accurate, assuming they are of the same quality. You will also need a good depth micrometer, a set of feeler gauges, and a set of thread gauges.

You will also need two good quality dial indicators, accurate to one ten-thousandths of an inch (.0001”) to allow you to precisely center the bore of your barrel blank in the bore of the spindle. If you are just starting out as a gunsmith, I would suggest you do not skimp on your tools or you will find yourself buying better tools later on as your skills improve. Buying good tools first will save you money in the long run, and will allow you to produce the best work product you can.

In addition to these measuring devices, you will need a piloted finish reamer for the caliber you wish to create, a floating reamer holder, a set of pilot bushings for that reamer, a set of range rods, a “Grizzly Rod,” and a GO gage. You do not need a NO-GO Gage. All of these items can be obtained from a number of manufacturers. I happen to buy my reamers and related tools from Pacific Tool and Gauge, but there are many other good sources.

Taking the Measurements You Will Need

The first thing you need to do is take a number of measurements from your blueprinted action so you know what dimensions you will need to reproduce when working on the chamber end of the barrel. For these measurements, you will need a micrometer, or at least a good set of calipers, a depth micrometer, your blueprinted and stripped Remington 700 action and bolt, and the recoil lug you will be using.

I would strongly suggest you purchase a competition recoil lug. These are thicker than Remington’s version, and are Blanchard ground so they are precisely parallel and the same thickness over the entire surface area of the lug. Darrell Holland produces an excellent competition recoil lug. Again, they can be obtained either from Brownells, directly from Darrell Holland, or from a number of other sources.

With the stripped bolt in the stripped action, place the action into your padded vice in a vertical or upright position, being sure the bolt is free to move up and down, but not fall out. Next, place the recoil lug onto the face of the action in the position it will occupy, and check to be sure the bolt can move up and down freely.

Now, close the bolt and use your depth micrometer to measure the distance from the top of the recoil lug to the front of the bolt lugs, to four decimal places (for example, .9575) if you are able. From that dimension, you must now subtract an amount that will give you some clearance between the bolt nose and the face of the breech. The amount to subtract will depend upon the caliber and the use to which the finished product will be put by you or your customer.

Measuring the action

For a big game rifle, I leave .006” to .008”, to be sure the rifle will not be disabled by a little grit or a small bristle from your cleaning brush. Watching that big buck going over the top of the hill because you can’t get your bolt closed would not be good, and your customer would likely be upset, and rightly so. When building a target rifle or a varmint rifle, I tighten things up quite a bit and subtract only .002 of the tenon you will be cutting on the barrel blank.

The next measurement we must take is the distance from the top of the recoil lug to the face of the bolt. Again, try to work to four decimal places if you can. From this figure, we must subtract .002 to allow for the torque when putting the barrel onto the action. The resulting dimension is the total headspace. When we get around to cutting our chamber, I will discuss two ways to set the proper headspace, only one of which requires knowing this dimension.

For the remaining two measurements we must take, we are going to remove the action and bolt from the vise, remove the bolt from the action, and put the bolt face up in the padded vise. Now measure the distance from the front of the bolt nose to the front of the bolt lugs, and add the same amount you added to get your tenon length (.002” to .008”). This will give you the total depth of the counter-bore you will need to cut in the breech end of the barrel blank for the bolt nose.

The final measurement we must make is the bolt nose diameter. To this figure, we must again add the same amount that you added to get your tenon length (.002” to .008”) This will tell us what diameter the bolt nose recess we cut into the breech end of the barrel blank needs to be.

Measuring the bolt nose

At the end of Part Two of this article you will find a form I use to keep track of all of these measurements. If you take these measurements carefully you will be able to chamber another barrel for your customer without even having the action available to you, and it will be a perfect fit.

Barrel Set Up

The first thing we must do is set up the barrel in our lathe with the breech end of the barrel protruding through the jaws of our four-jaw chuck far enough that no part of the barrel that will become the chamber is within the area clamped by the chuck jaws. The purpose of this positioning is to assure no pressure is put on the area where you will be cutting the chamber. You would be amazed to learn how much pressure can be applied by the jaws of a chuck. Too much pressure on the chamber area could cause deformation of the chamber. Surely the deformation would be very slight, but when you are looking for the greatest possible accuracy from your rifle or a customer’s rifle, everything must be perfect. Little things matter a lot.

I always work on barrels through the headstock, rather than between centers. I believe this is the best method for achieving the most accurate results. Certainly, some might disagree with this approach, but it is the way I do it. However, if your lathe does not have a large enough spindle bore to allow you to do your barrel work through the spindle, then you will have to do it between centers.

I have made a set of lathe jaws for barrel work which I have notched by first installing them on the four-jaw chuck, and then notching them with an inside threading tool fairly deeply. This will allow the use of a circular brass rod cut to fit the diameter of the barrel you are chambering. The brass rod goes around the barrel and then locks into the groves in each of the four jaws of your chuck. This will hold the barrel securely and still allow it to pivot as the muzzle end of the bore is centered in the spider.

Breech end set-up with brass ring

Another way to secure the barrel and still allow it to pivot, as it must, is to use four small pieces of aluminum that have been bent at 90 degrees, placing one under each of the four jaws. Either way will work quite well.

Aluminum pivots

Now it is time to position the barrel blank within the spindle bore. Begin by visually centering both ends of the barrel blank using the four-jaw chuck on the breech end and the spider on the muzzle end. Now find out which of your pilots from the pilot set you purchased will fit tightly into the barrel bore but still moves freely into the bore. You will need one for each end of the barrel blank. Once you have found the two pilots that fit best, secure one to each of your range rods and insert one of the piloted range rods into each end of the barrel as far as it will go. The range rods are tapered very slightly and will only insert part way into each end of your barrel blank.

With one piloted range rod inserted as far as possible into each end of your barrel blank, position your one tenthousandth (.0001) dial indicators so they will read the position of each range rod relative to the center of your spindle bore. Now adjust the spider and the jaws of your four-jaw chuck so that both dial indicators read .0000 as you rotate the chuck by hand. It does not really matter which end you start with. I usually start with the breech end, for no particular reason. Keep going from end to end until you are satisfied that each end of the bore of the barrel blank reads perfectly true. This can take some time, especially the first few times you do it; but keep working at it until you have it with .0000 readout on each end.

Dial indicator on breech end

Spider on spindle

This is pretty much the way barrels have been dialed in for years, and most gunsmiths will stop here, but a riflesmith named Gordy Gritters has perfected a further procedure which will assure your chamber is cut precisely in line with the bore.

The problem is the bore of your barrel blank is almost never perfectly straight and centered in the barrel blank. So, even if you have both ends of the barrel blank perfectly dialed in, a curve in the bore of the barrel blank can cause your tenon, threads, and chamber to be cut at an angle to the bore of your barrel blank. The drawing above is, of course, greatly exaggerated to show the problem more clearly.

Fortunately, Gordy Gritters of Extreme Accuracy Institute, has developed an excellent way to deal with this problem. You need to install your best fitting pilot to the end of the proper size “Grizzly Rod” and place the other end into a chuck in your tail stock. Now run your tail stock up until the pilot on the end of the “Grizzly Rod” is just inside the bore. Position one of your .0001” dial indicators against the top of the “Grizzly Rod,” near the end of the barrel, and dial it in using the spider at the muzzle end of the barrel blank. Then move the “Grizzly Rod” a few inches into the bore and dial it in again using the four-jaw chuck.

Using the Grizzly Rod

Our goal here is to dial in the breech end of the barrel blank so that while moving the “Grizzly Rod” into the bore the entire distance from the beginning of the bore to a point about two inches past where the chamber will end, there is no run out on the rod.

It is important to note we do not care what is happening to the muzzle end of the barrel blank. All that matters is the chamber area and a couple of inches beyond the chamber are perfectly aligned with the axis of your lathe spindle. You will find an excellent and very detailed video explaining this method of dialing in a barrel, entitled “Chambering a Championship Match Barrel,” on Gordy’s web site. I would strongly urge you to invest in this video.

Cutting and Threading the Tenon

Now that we have our barrel blank properly set up in our lathe, we begin by facing off the chamber end of the barrel blank. Cut the tenon approximately .010” to .015” longer than the tenon length we determined when we took our measurements of the action and recoil lug. For the Remington 700 action we are using, the diameter of the tenon will be 1.0625. But the best practice is to decrease the diameter of the tenon until the recoil lug will just fit over it and spin without restriction. Now face off the breech end of the barrel blank to obtain the precise tenon length desired. Finally, use a very sharply pointed tool to undercut the shoulder you created when you turned the tenon. Undercut the shoulder as closely as possible to the tenon to remove any possible radius that may have been left by the cutting tool you used to cut the tenon.

Cutting the tenon

Now that the tenon is cut correctly, we must thread it. Before threading the tenon, I find it helpful to cut a slight 45-degree chamfer on the end of the tenon. For our Remington 700 action we will need to set our lathe to cut 16 threads per inch.

You may cut the threads in whatever manner you have learned. I cut threads in a somewhat different manner. I will make no attempt to discuss how to cut threads, but this is a skill that you must master before you try to cut threads on a barrel blank. I cut my threads upside down and backwards, so to speak. I run the lathe in reverse, turn my thread cutting tool upside down, and cut from the shoulder to the end of the tenon. I find this method far easier to use.

Cutting threads upside down and in reverse with upside down threading tool.

However you cut threads, the action should start fitting when they are about .042 to .043 of an inch deep. A good way to determine the depth to which you need to cut threads before they begin to fit is to divide .695 by the number of threads per inch that you are cutting. In the case of a Remington 700 action we are dealing with 16 threads per inch. As a result, the math looks like this: (.695” ∕ 16 tpi = .043”). Your threads should be just the tiniest bit loose so the action will tighten absolutely square to the recoil lug.

Finished tenon with faced and beveled end

Now that you have cut and threaded your tenon exactly to the measurements you took of your action, you need to use a boring bar to cut the recess in the end of the barrel for the bolt nose to fit into. Here, again, you will be using the measurements you took earlier for the depth and the diameter of the recess. Now screw the action, with its recoil lug, all the way onto the barrel and insert the bolt into the action. The bolt should go all of the way into the action, and the bolt handle should fall into the down position without any resistance.

To be continued . . .


2 Responses to Fitting and Chambering a Custom Barrel—Part 1

  1. Super awesome Joe!!
    Would love to practice doing this sometime on a short, scrap piece of round-stock (aluminum or steel) that will fit into my mini lathe. The lathe is certainly not a pro-grade set-up but it will be great to practice some things when I find some material to work with.
    Excellent article! Thank you Sir!
    Cheers

  2. Will you please give me an estimate of the normal charge to blueprint a Remington 700 action and fit a barrel to the action. I see that some barrel manufacturers sell pre-chambered barrels and wonder if you are ok with using someone else’s chambered barrel or if you will only fit a barrel that you have chambered.

    Thanks

Leave a Reply

Your email address will not be published. Required fields are marked *