Precision Barrel Fitting, Part Two

In Part One we introduced The Complete Illustrated Guide to Precision Rifle Barrel Fitting by John Hinnant, a superb book on barreling. By now, I hope you have either made or purchased a barrel vise, one of the two indispensable hand tools required. The second indispensable hand tool is a receiver wrench. A strong, well-constructed receiver wrench is every bit the necessity as the vise and must be even more flexible in its design to be adaptable to a multiplicity of rifles.

In two areas, the fabrication of the vise and wrench share methodology. The wrench jaws are made the same as was outlined for the vise base and sliding plates. To repeat myself, drilling and boring for wrench jaws mirror the preparation of vise clamp blocks. The bored dimension illustrated matches the diameter of the Kleinendorst Remington 700 barrel tool that is available from Brownells. The tool holds the recoil lug in alignment when installing the barrel.

If you work exclusively on Model 700 rifles you’ll never need different wrench jaws, however, there is no sound reason why you should limit your capabilities and your business to only fitting rifle barrels to the Model 700. I have a sound reason to believe every one of our members is aware all rifle receivers aren’t round like a Remington. Some are round at the top and flat on the bottom.

In these cases the bushing has to be turned to the correct outside diameter—not bored to that diameter—then split in half, fit into one of the wrench jaws and filed or milled flush. The Ruger 77, Sako and Shilen DGA require two flat jaw bushings. The same is true for lever and single shot actions. You see, using a receiver wrench capable of accepting different configurations between its jaws, as does the design offered by Brownells, opens your door to a near limitless list of rifle lovers.

Just as important, these receiver wrench bushings should be made of steel, not aluminum. In making a universal wrench, note a receiver wrench is going to take a lot of abuse and may demand a length of pipe be slipped over its handle to provide more torque in getting tight barrels started. The handle is fabricated from husky bar stock. It must never be threaded to fit a hole drilled into a jaw. Doing so can further weaken what already is a comparatively weak area.

The handle must have a heavy duty weld holding the jaw in place. An alternate wrench design uses no bushings—meaning it cannot be considered universal— and can double as a reamer wrench. The subject of reaming and finishing a chamber will be discussed in a future article at which time this wrench and duplicates of it will be discussed in greater detail. Going Lathing As illustrated, the basic lathe set-up is shown. The bed of the machine should be long enough to hold the barrel as dictated in the drawing.

Note, the captions refer to a relief shoulder. Said shoulder is created when a cut has been made at the muzzle to recess the land and grooves of the rifling. This recessing protects the extreme muzzle end of the rifling from dents and dings. All target rifle barrels have this recess. There is nothing quite like having a bullet come into contact with damaged rifling just as it departs the barrel to assure it will fail to strike the point at which it was aimed.

How to make this protective cut will be shown in a separate article. Another reason I bring up the relief shoulder is due to the fact that the shoulder, while critical to accuracy, thins the end of the barrel. Ergo, never squeeze the barrel between lathe head stock jaws by its relief shoulder. To make that perfectly clear, yours truly has shaded the area between the jaws.

Consider it the forbidden zone, the rifle graveyard or simply a big "no-no." In the illustration on short bed lathe set-up, all the warnings just made have been ignored. How come? When the lathe bed is too short to accommodate the set-up described before, the muzzle end of the barrel has to pass through the head stock. In these cases you must protect the barrel surfaces held between the jaws.

You can either wrap a single thickness of masking tape around the barrel or snip out aluminum, brass or copper shims from uniformly-thick pieces of stock to be placed between the jaws and the barrel surface. I think a few words about head stock jaws are in order. A universal, three jaw, self-centering chuck with 0.001-0.002 of repeatable capability is accurate enough in many ap-

You’ll learn more of them as this series progresses. plications. If the three jaw cannot meet those specifications a four jaw chuck is recommended. They make it possible to center a barrel within plus or minus 0.0005 or less. When consulting with your lathe provider make the source fully aware of your requirements. Some notes for tuning metal between centers.

Though the face plate and lathe dog method is a common means of working over apiece of metal, when the metal being worked over is a barrel it is not recommended. The tailstock live center—the best among them are of the bearing variety—must always be used as support. Without it, the barrel will fall off the face plate. Since moving the tailstock center away from the barrel is required in some fitting and chambering steps, this departure of the work piece can run up time in reestablishing set up.

One major problem with multiple set ups is the possible loss of, or at least a fluctuation in, the indicator. To lessen or totally free operator concerns, a collet inserted into the headstock chuck is considered superior to any other method of holding a barrel and is very accurate. Collet use will not eliminate use of the steady rest to avoid tool chatter and the barrel relief cut must be turned to match the size of the collet.

Always remember, the barrel is not removed from the lathe until all fitting and chambering steps have been completed. Lapping Bolt Lugs Why the detail so vital as lapping bolt lugs in rifle work is ever overlooked or omitted on barrel fitting jobs makes me wonder if it happens due to a forgetful practitioner or a lazy one. I’ll make this pretty simple. Lapping bolt locking lugs to mate evenly in the receiver is related to both accuracy and safety.

Pay close attention to how the end of the work piece is not held in position via contact with the lathe chuck jaws. One reason is mentioned in the text. There are others. More rifles than you’d suspect are made with only one bolt lug. That is never as safe as a rifle with two lugs. How those two lugs bear has an adverse effect on accuracy. Every serious rifle shooter from bench rest competitors to trophy hunters to the seasonal seeker of meat for the family freezer would agree on that.

It is specifics on accomplishing this they might not know. The next paragraph provides the "what" you can tell them from now on. When you do you’ll be moved to a higher place in their opinion of you as a person who really knows the inside story of rifles. Feel free to make notes regarding twin lug bolts. When both lugs fail to make uniform contact with the main portion of the cartridge thrust uneven pressure is transferred to the receiver.

If the lower lug is the only one contacting, the receiver bows upward at its ends. If only the upper lug is the culprit, the receiver leans toward bowing up in its middle. In either case, the barrel is affected and so is the point of impact. The included illustration can serve as a guide to making a bolt lapping tool. The only specification not subject to deviation in the fabrication is the receiver thread. All others can be modified.

The sleeve can be turned from any type of bar stock including low or medium carbon steel. A visit to a salvage yard

The barrel has to extend beyond the head stock. The drawing points out the measure to be taken in avoiding finish damage to the barrel. might turn up a soft piece of stainless steel. Despite the rust resistance gained, some opinions hold stainless is too hard for machining. However, if the piece selected can be filed easily it can usually be machined in a conventional manner. The spring loaded plunger can be turned from steel, brass, copper or Delrin plastic. Aluminum can be used but it wears rapidly.

The spring itself should only provide moderate pressure. Too much spring tension makes the bolt hard to operate during lapping. In addition, excessive tension can force the bolt out of alignment with the receiver. Checking bolt lugs for uneven bearing is quite easy. Coat the rear of the lugs with layout dye and allow to dry. Insert the bolt in the lapping tool. Thread the unit in the receiver. Close the bolt. Using the tool, apply light to medium pressure and push the lugs against the receiver locking recess.

Withdraw the bolt. Layout dye will have been scraped off the rear of both lugs if both are bearing. Frequently, only one lug is partially bearing and the other not at all. When more than two lugs are involved it’s not unusual to discover lugs bearing evenly on half or fewer. To even the lug contact, clean off the layout dye and coat the rear of the lugs with 120 grit lapping compound. Open and close the bolt 10 to 20 times. The receiver can be held between the padded jaws of a bench vise during this action.

Remove the bolt and check the rear of the lugs. If all are bearing evenly their rear surfaces will be uniformly polished. Repeat the polishing until they are. Then and only then are the lugs properly seated. Wash off any remaining lapping compound and consider the job finished. A few words of caution about Mauser 98 rifles. The receivers of these rifles were machined from tough, high quality but low carbon steel. The finished receiver was then carburized (case hardened) to give them a hard surface with a soft core.

Normally, the bolts were made of medium to high carbon steel and then hardened to a higher degree. Fortunately, most 98 actions with matching serial numbers on their bolts and receivers will not require lapping. They’ve been shot so much over the years the bolts have been set back and the lugs seat properly. The exception to this turn up with various Mauser 98s produced for South American countries. They are very soft. How far the lugs will set back before finally seating remains an open question.

Complicating things further, it may not be possible to reheat treat their receivers without repeating the carburizing process. A carburized surface isn’t very thick. It’s not difficult at all to lap through the hardened part and into the softer metal beneath it. Hardened bolt banging into a soft receiver? Uncertain heat treatment? My answer to those concerns is a recommendation against any willy-nilly lapping of 1898 Mausers that weren’t made for the Wehrmacht. AG