Precision Barrel Fitting, Part Four

What follows here can only be considered a beginning to barrel prep and installation, and gives me an additional opportunity to recommend the purchase of the third edition of John Hinnant’s book, The Complete Illustrated Guide to Precision Rifle Barrel Fitting. How to and where are listed at the end of this article. It may surprise you to see Dave Manson being identified as a source. Well, it shouldn’t.

Dave plays an important role in Hinnant’s content as most of it involves chambering, rechambering and crowning a barrel. How to do all three are described by John Hinnant inclusive of a lathe, however, and further includes how those vital steps can be accomplished equally well with hand tooling manufactured and supplied by Dave Manson. I never claimed this series to be a substitute for the book’s total content. An encouragement to own it? For sure.

Couple that with a polite plea to somehow, some way, rack up enough hours working with a lathe. There is no substitute for eliminating any concerns about your ability with machine tools other than getting to know them. I’ll only offer a single, very large warning: Never be wearing a necktie when you turn on a lathe. Way, way back in my high school shop days one classmate of mine had tucked his tie into his shirt.

It fell out and began wrapping around the workpiece, fortunately being turned at moderate speed, between centers. Mr. Dudley, the shop teacher, was standing next to the kid, saw what had happened, whipped out the very sharp hunting knife he habitually wore on his belt, slashed the tie cleanly in half and my friend straightened up with his nose still attached to his face. Nobody ever wore a tie in shop class after that. I’m also betting nobody challenged Mr. Dudley to a knife fight, either.

A three-jaw chuck with repeatable centering capability is permissible. A four-jaw is preferred. Perhaps the necktie warning comes as unwarranted where you are concerned but precision barrel fitting is a process not to be casually plunged into. There’s simply too much to learn beforehand. Besides the oft-mentioned Hinnant book, there is Gunsmithing by Roy Dunlap and How to Run a Lathe published by South Bend Lathe Company. Through your own research you’re likely to discover other pertinent reading. Don’t avoid it.

If there’s anything I’ve learned about this business it’s you can’t afford to stop learning, you’ll never learn enough and no one person will ever know all there is to know about every kind of firearm. Regardless of your knowledge, you will certainly hear your share of "I heard that…" or "I read somewhere that…" expressed in opposition to almost any resolution you offer on the repair or improve-

In the process avoid taking off excessive material. A too-thin barrel can become crushed under lathe jaw pressure. It is rarely, if ever, required with an OEM barreled action. ment of a gun. Possibly they will be spoken of the rifle just handed you. Ask questions up front. Leave no question unanswered or in doubt before starting a rebarreling job. A first question to ask, is your customer OK with a barreled action from the original manufacturer or is a custom barrel demanded?

If the latter, it will mean you will be accumulating more billable man and machine hours and a higher end cost to prep such a barrel for fitting up. You can reduce the hours by choosing a maker well known for providing perfectly straight barrels with rifling well defined inside a dead center bore, precisely chambered and in the desired configuration, such as tapered, fluted or target. Ask around if you have doubts. The Brownells Techs will have suggestions. So will widely experienced gunsmiths.

To get you started, I’ll mention three makers you should consider: Shilen, Shaw and Mac Millan. There are others to be considered of course. A couple are mention in the Hinnant book. The importance of choosing a barrel provider cannot be overstated. Choose wisely and don’t rush into the choice uninformed. While I avoid making that choice for you, I insist on making one regarding a dial indicator. Buy one.

It will be indispensable in assuring the precision of all your turning operations and you can apply it in checking how straight the barrel appears to be. A Mitutoyo or Starrett indicator with +/-0.0005 capability is recommended. You can either mount it on the tail stock of a lathe as shown in the Hinnant book or, as I prefer, mount it on a magnetic base that can be moved easily along the length of the barrel before it firmly grabs on to any magnet-receptive point in the working area.

That includes the metal table on which the lathe is mounted. These magnetic bases can be found on the web. Search for "Starrett Machine Tool Indicators." When a lathe with along bed still lived in my shop I used to check barrels for straightness by placing the indicator in contact with the barrel exterior just short of the muzzle and turning on the lathe. If the indicator showed any wobble more than +/- 0.01 the barrel was returned to its maker for replacement and/or

straightening. You may elect to be more or less demanding. With either one of the indicators mentioned you have the flexibility, and the luxury, of setting your own standards. Making Barrel Relief Cuts In case you missed or misplaced the previous issue describing them, there are two basic lathe setups for turning a relief cut. The first is done using along bed lathe. Here the muzzle end of the barrel is held in the lathe chuck. The shoulder of the cut avoids slippage of the barrel through the chuck jaws.

The OAL of the cut should match the jaw length. Avoid making cuts shorter than this. Short cuts can cause longitudinal springing of the jaws, possible jaw damage and a resulting loss of centering accuracy. The diameter of the cut doesn’t present that particular problem. It presents another. Turn off too much material and you may end up with thin barrel walls. If ex- American Gunsmithing Association

Any departure from perfection can result in lessened accuracy and reliability. The cutting tool should be given a left hand turn to form an angle of five to ten degrees. The indicator above is mounted on its magnetic base and can easily be moved to any magnet-receptive work area. cessively thin, these can be crushed under lathe jaw pressure. When no long bed lathe is involved omit the long bed lathe setup and use a set up for a short bed lathe instead.

A three-jaw chuck is permissible as long as it centers accurately but a four-jaw is recommended. Another three-jaw alternative is the use of a collet in which case the cut diameter must match that of the collet. Turning The Breech O. D. These instructions will apply if the decision is to fit up a barrel blank rather than an OEM barreled action. Unless your operation has machinery capable of drilling bores and rifling accurate bores, I doubt you will be working with a total blank.

You could, however, be faced with a bored, rifled, but otherwise untouched one. If that be the case turn the breech to the correct diameter plus 0.025-0.030 inches. In the turning, position the steady rest as close as possible to the work area of the barrel. Avoid positioning the rest so close it interferes with movement of the carrier and cross feed movement of the compound rest. Tenon Length When marking the thread tenon length, the end of the breech point should match the shoulder length of the cartridge case.

This can be determined using an outside caliper or micrometer as a gauge. Open either measuring tool to the finished, major breech outside diameter. Safe sporter barrel standards for this diameter in many of the more popular calibers appear in Gunsmithing by Roy Dunlap and are included in the Hinnant book. Slide the gauge you have fabricated up the barrel until it stops. That’s point "X," the place where the downward configuration of the chamber ends and the taper toward the muzzle begins.

The length of the tenon should match the depth to which the threads reach within the receiver. Turning Tenon Diameter Make no change in lathe set up from its breech turning operation. The tenon should be turned 0.025-0.030 larger than its finished diameter. Note that a cutting tool should be given a left hand turn to form an angle of five to ten degrees. A corresponding angle will be cut on the breech/tenon shoulder.

Since the tenon must match perfectly with the receiver, and the receiver has previously been precision faced, the angle just cut on the tenon must now be faced to a matching 90 degrees. In this facing operation, do not allow any left or right longitudinal movement of the cutting tool. On page 65 of his book, Hinnant describes two means of preventing any movement. The importance of achieving a square tenon shoulder can’t be overemphasized.

After threading, a properly-fit barrel must be tightly butted against the receiver. Any deviation in a perfect relationship between the tenon shoulder and receiver face prior to uniting the barrel and receiver will prevent the union from being 100%. In Part Five, muzzle crowning, making the extractor cut and assembly of the barrel and receiver will become the focus. Chambering will get most of the attention in Part Six and include the .22 LR cartridge.

Part Seven will address blue printing a rifle, including an update on the same subject. Contacts John Hinnant, johnsharonhinnant@ sbcglobal.net Dave Manson, Manson Precision, AG