Fitting and Chambering a Custom Barrel—Part 2

By Joe Fischnaller, Owner
Moses Lake Custom Rifles, GCA Member

(continued from last week)

Cutting the Chamber

We are now ready to cut our chamber into the barrel. It is a good idea to use a drill bit to begin the chamber cut. You want to use a drill bit that is approximately three-quarters the diameter of the forward portion of the body of the chamber reamer you will be using, and you only want to drill to a depth about three-quarters the depth of the chamber you will be cutting. This will help make your chamber reamers last longer.

Now set your lathe to whatever speed is recommended by your chamber reamer manufacturer. I tend to use a speed of 250 rpm for most chambers when using a high-speed steel reamer. Carbide reamers can run at higher speeds. Install the best fitting pilot you have onto your chamber reamer, attach the piloted chamber reamer to your floating reamer holder, and install the assembly into the tailstock of your lathe. Squirt some cutting oil onto your chamber reamer and into the breech end of the barrel. Do not skimp on the oil. Use plenty of oil and use only a good quality cutting oil. I use Rustlick 711 which is no longer available, but I still have a small supply of it left.

Now, carefully move the tailstock forward and the reamer into the recess you have drilled in the end of the barrel until it is fully inserted. When you are sure your piloted chamber reamer is inserted as far as it can go, lock down your tailstock, back the reamer out slightly, and start your lathe. For your first couple of cuts, you can take perhaps .100.” When you have taken as deep a cut as you are going to, stop the lathe while the reamer is still all the way into the chamber, and remove it only when the lathe has stopped completely. This will insure you do not roll a chip and scar the chamber wall. As your chamber reamer begins to cut more metal, decrease the depth of your cuts to .050,” and later to .020” or so. The idea is to be absolutely certain your cuts are not so deep the chips pack solidly and you run the risk of rolling a chip and scarring the chamber.

Floating reamer holder and chambering reamer

As you get near the end, you will want to creep up on it very slowly and carefully. Check headspace as you go by threading the stripped action onto the barrel, and inserting the stripped bolt into the action. Now open the bolt and insert your “Go Gauge” into the chamber and attempt to close the bolt. The bolt should not close. Now unscrew the action just until the bolt will close, and no more. Use your feeler gauges to determine the distance between the face of the action and the tenon shoulder on the barrel. If this is less than .020” you can take it in one final cut; otherwise take two or more cuts as may be required. You do not want to take too much.

Earlier, I promised I would show you a second way to check your headspace. First you will need to turn an aluminum or brass sleeve that will fit over the threaded end of your barrel and butt up against the shoulder of your tenon. Both ends will need to be absolutely square and parallel to one another. The length should be approximately 2.00 inches or at least a little longer than the headspace measurement you determined during the measurement phase of this project. You must know the exact length of your sleeve, to four decimal places. Now, if you place the sleeve over the threaded tenon, and put the “Go Gauge” into the chamber, you can use a depth gauge to determine if the headspace is correct. Just subtract the distance from the end of the sleeve to the back of the headspace gauge from the exact length of the sleeve. The result needs to exactly match the headspace measurement you took earlier.

At this point, you can screw your action quite tightly onto your barrel and insert the “Go Gauge” into the chamber. Now insert the stripped bolt into the action and close it. The bolt should not fall down on its own. It should require approximately one pound of pressure to push the bolt handle down. If it does, you have done a great job of chambering the barrel. Just to be sure, now put two layers of cellophane tape (approximately .004” in additional length) on the back of the “Go Gauge” and trim around the edge of the “Go Gauge”, thus converting it to a “No Go Gauge”. Insert the newly created “No Go Gauge” into the chamber and see if the bolt will close. It should not even start to close. When you have achieved this “0” headspace, remove the action from the barrel and give yourself a pat on the back.

We need to polish the chamber now, but first put a slight chamfer on the entrance to the chamber and on the entrance to the bolt nose recess. The chamfer for the chamber entrance should be very slight. I would suggest it be only .060” to .070” at the most. The chamfer to the entrance of the bolt nose recess may be somewhat larger; perhaps one-eighth of an inch (.125”) or so. Begin your chamber polishing by carefully inspecting your chamber to determine how much polishing it will need. Often, you will have some minor tool marks that need to be removed. Depending on the quality of the chamber you have cut, you may want to start with a 320-grit wet/dry sandpaper wrapped around a short piece of dowel of the appropriate diameter, with the lathe turning at around 1000 rpm or so. You should use the 320-grit sandpaper sparingly; you do not want to enlarge the chamber at all. Next, progress through 400, 600, and finally 1200-grit wet/dry sandpaper. This should give you a beautiful chamber. You are now through with the breech end of the barrel and ready to begin work on the muzzle end.

Crowning the Barrel

Now turn the barrel around on your lathe, so you can work on the muzzle end. Set up the muzzle end of the barrel in your lathe in exactly the same manner as you did with the breech end, including the use of a Grizzly Rod for the final adjustments to be sure the muzzle end of the bore is precisely parallel to the axis of your lathe. If you fail to do this perfectly, the crown that you cut will not be precisely perpendicular to the bore, and accuracy will suffer. Usually the last inch or so of the muzzle end of the barrel is not of the same quality as the rest of the barrel and should be removed. In any event, you will need to cut the barrel to the length your customer desires.

Cutting the crown

There are several acceptable types of crowns for your customer to choose from. They include an 11-degree target crown, a recessed crown, and a quiet crown. Many years ago, the Army Marksmanship Unit spent a lot of taxpayer dollars to determine the most accurate crown for target rifles, and came to the conclusion that an 11-degree crown was the answer. Virtually all benchrest shooters have their rifles crowned in this manner. In benchrest matches, if your group opens up by only a couple of thousandths of an inch, you can go from the top of the results board to being an also ran. By far, the majority of the rifles I build are crowned in this manner.

The recessed crown is usually a crown cut straight across the muzzle, but slightly recessed to protect the crown. Many factory rifles have this type of crown. A variation of this crown is the quiet crown, which is simply a deeply recessed straight crown. The deeper you cut the quiet crown, the quieter it will be. They can be very helpful for the hunter who does not wear any type of ear protection while hunting. The quiet crown directs the sound down range rather effectively. If your customer wants a muzzle brake installed for shooting at the bench, but also wants a thread protector for times he is hunting and not using the muzzle brake; you might want to ask him about extending the thread protector an extra inch or so beyond the end of the muzzle to provide a good amount of sound reduction for the shooter.

Once you and your customer have decided what type of crown you want, cut it, but very carefully, since any burrs you leave can cause problems. I use a Q-tip to check the crown, which should be very sharp, but without any burrs. If you place the Q-tip into the crown area and turn it, you will find any burrs you may have left. If you find any burrs, re-cut the crown. Now that you have cut the perfect crown, you should slightly round the outside edge of the muzzle to the extent you find aesthetically pleasing.

Polishing the Barrel

The final step in preparing the barreled action for bedding in a stock is to put a finish on the barrel. You should discuss the extent of polish desired for the barrel with your customer. A benchrest shooter or a varmint hunter having you build a prairie dog rifle may want a highly-polished finish, while some hunters will want a stainless barrel finished to a somewhat courser degree, or bead blasted.

Make an aluminum sleeve and screw on cap for the breech end of the barrel. The sleeve should have a diameter somewhat larger than the diameter of the bell of the barrel so it prevents the sanding block used to finish the barrel from rolling over the unthreaded breech end of the barrel which butts up against the recoil lug of the action. The cap should screw onto the breech end of the barrel and hold the sleeve firmly in place. These two items will give you a way to hold the breech end of the barrel in the lathe’s 4-jaw chuck during the polishing process.

Aluminum collar and cap, and Delrin plugs

You will also need a way to hold the muzzle in the tailstock of your lathe during the polishing process. The best way I have found to accomplish this is to turn some small Delrin pieces with one end that fits tightly into the barrel, and the other end with a 60º cut to fit over your live center. This will allow you to hold the muzzle end of the barrel securely in place during the polishing process.

During the processing of the barrel, either by the manufacturing process or during your work on the barrel, it is likely some dings or scratches will have found your barrel and need to be removed. This will occasionally require 220 grit sandpaper, but usually 320 grit will suffice. Just be sure you eliminate all of them, so your product looks like a real gunsmith did the work and not a blacksmith. Be sure to use a sanding block for all of this finishing work.

Once all of the tool marks and nicks are gone, continue to use progressively finer grades of sandpaper until the finish is what your customer desires. You can go all the way to 1200 grit if you want a very shiny finish. If you want an even brighter finish, you can use Flitz to polish the barrel, or even jeweler’s rouge. You are now finished and have created an excellent barreled action that will produce a superbly accurate rifle once it is properly bedded, stress free, in a quality stock. You should be aware some cartridges will naturally be more accurate than other cartridges. As a result, you should be careful in guaranteeing your customer a given level of accuracy. If you have done a good job in blueprinting the action, fitting and chambering the barrel to that action, and bedding the barreled action into a quality stock, you can rest assured the rifle will be as accurate as it can be, allowing for the cartridge and the skill of the shooter.

One Response to Fitting and Chambering a Custom Barrel—Part 2

  1. Wow, what a project. Really gotta know what you’re doing start to finish, no doubt.

    I like the spec sheet at the end. I think this is what Darrell Holland hand wrote on a sheet of paper in his AGI Super Tuning the Factory Rifle DVD course. I have watched about half of it during the past few days. I’ve seen up to where he will begin chambering the Rem 700 barrel. Up till there it seems to match up with what Joe has here.

    Thanks for an awesome, in depth article Joe.