Precision Barrel Fitting, Part Seven

My assumption that the sheer cost of full length barrel boring and rifling machines plus the space required to house them will not exclude requests you rechamber a rifle remains unchanged. All that is required to fulfill these requests area well-made, consistently-accurate machine lathe along with a couple of additional items proven to be precision tooling. Whether the work piece is an OEM or aftermarket action, the most expressed wish is for a change in caliber.

Among the more experienced, including serious hunters and High Power rifle competitors, the chamber switch will often be accompanied by a second request to blueprint it as well, along with a test target showing the results. The rifle owner giving out those instructions wants you to believe you’re dealing with a no-nonsense shooter. These requests cost plenty and the person making them knows that. Or should. So should you. The tooling used and illustrated in this article totals out at slightly over a grand.

That cost can of course be spread out over a number of rifle overhauls. In that respect, it partners with the purchase price of your lathe and figuring the time required to get the entire job done. There’s no how, no way, atop notch chambering request happens on the cheap. Exactly the same can or should be said of blueprinting.

When you receive a request for either, or both, I suggest you don’t rush to enter the object into your records until you have determined the request to be possible, will achieve the desired objective, be fully paid in a reasonable span of time and, most importantly, be safe. Providing an example or two serves to underscore the last requirement. I remember the day I was handed an original 1873 Trapdoor Springfield in .45-70. The owner wanted to switch to .45-90.

He turned a deaf ear to all advisory words warning him the alteration would drastically drive down the value of the old beauty. He was going after large, dangerous game and wanted nothing less than .45-90. I managed to regain his attention with the notification he had handed over a .45-70 Trapdoor carbine.

In cavalry use the carbine had never been charged with more than 55 grains and that by increasing the charge more than a third in a 107-year old timer could be fatal to him while doing nothing but alert the trophy Grizz or Alaskan Brown he wanted on his list of previously taken game that he was in the area. If he were close enough, either might charge and maul him just for making such a ruckus. That commentary was heard loud and clear. The Trapdoor remained untouched except for a thorough cleanup.

The owner of the trapdoor was not exceptional in his lack of retained knowledge about the gun. Another example can be given regarding the owner who wanted a chamber reduction. His wish was to lessen the recoil of his wife’s lightweight .30- 06 hunting rifle to .223. I informed him that lightweight rifles in larger calibers have a kick to match and that reducing the caliber could well reduce the kick.

I was self-inspired to add that sending a 0.24" diameter slug rattling down and out a 0.30" diameter bore would be highly unlikely to seriously impact the object at which she had shot. Wound? Maybe, but not immediately fatal. The husband, wanting his hunting partner to remain a happy hunting partner, traded in the .30-06 on a neat Sako in .243. I saved a marriage and made a profit. It was a good day.

I had inverse but not dissimilar concerns when a known to me and (reportedly) experienced reloader asked that his own .30-06 be rechambered to .35 Whelen. His objective was for a larger diameter but not necessarily an increased bullet weight. While it is true the .35 Whelen case mirrors that of the .30-06, the .30 caliber bore diameter is smaller. I reminded him this difference would at least generate increased pressure resulting in back primer setback plus bulged brass and possibly a blown receiver or bolt face.

After thanking me for reminding him of a reloading factor he’d temporarily overlooked, the gent purchased several hundred large rifle primers and the same number of 168 grain .30 caliber HPBT jacketed bullets he had allowed to run low. Another customer walks away smiling. Another good day. Now that I’ve raised ared flag or two with which you should be concerned before logging in a chambering job, I’ll rely on your common sense to lock in to your memory as

The next article, part eight in this series, will be getting into blueprinting an action. Shown here is some of the precision tooling needed. Before whipping out your checkbook or credit card, note this tooling totals out at slightly over a grand. much as it will retain regarding interior ballistics and move right along. Reaming The Chamber Slow spindle speeds are required whenever reamers are in use. Going too fast is the most common cause of reamer chatter. Chatter is the sworn enemy of concentricity.

Lack of concentricity is a prime contributor to a lack of precision. Lack of precision always results in less accuracy. A means of reducing or totally resolving these concerns up front will be revealed shortly. The illustration showing chambering to a finished depth shows the lathe setup for reaming. The reamer handle is held in one hand while the other hand rotates the tailstock wheel to push the tool into the barrel. All reamers need liberal lubrication and frequent brushing off of metal chips.

Sulfur-based cutting oils are the best. Fill a small diameter plastic container with oil, brush off any metal chips and submerge the reamer in the oil. The practice of brushing off and rebaptizing the reamer should be followed every time a reamer is withdrawn from a barrel. That goes for any reamer. You may see or feel a slight oscillation as you feed in the roughing reamer. It’s not the problem it appears to be. Despite multiple corrective attempts to end this mini runout it has never been totally eliminated.

Fortunately, no chamber has ever been reamed oversize in diameter because of it. Ideally, a roughing and finishing reamer should be on hand for each caliber. Whassamatteryou, Blood? Reamers are expensive! Quite true, and while there is no substitute for a caliber-specific finishing reamer there is a perfect substitute for investing in an equal number of roughing reamers. It’s the Spiral Flute Interchangeable Pilot Roughing Reamer from Dave Manson Precision Reamers (MansonReamers.com).

That is quite a mouthful but as its lengthy product name hints, Dave’s rougher wears a caliber-specific pilot when it is inserted into the bore of a rifle being subjected to chamber work. Slide the pilot on to the cutter shaft, lube the cutter, insert the shaft into the bore and initiate reaming. These pilots make it possible to rough out many different calibers that are based on the same case design with a single reamer.

For example, a Manson .25-06 reamer wearing the appropriate pilot can go to work on a whole host of other calibers based on the .30-06 case. It’s the pilot that fits the bore and that maintains reamer alignment with the bore during the reaming process. A caution is in order. Beware of roughing a chamber too deep for the shaft of a finishing reamer to seat well in the bore. The shaft is the caliber specific end of the finisher. It replaces the pilot and must be allowed to complete a chamber all by itself.

Let’s discuss how to alternate roughing and finishing reamers during chambering, applying finishing and roughing reamers as a team. It is possible to initiate and complete a chamber job by using a finishing reamer exclusively but the practice is not universally followed. A major objection to it is that accelerated wear will dull the reamer prematurely. Countering that is the fact that double-teaming will save time.

The specific details of the process described in the next paragraph might tempt a disputing of the fact. Don’t bother. Once you have the know-how committed to memory no time will be lost. It will be saved. You begin with the rougher. When the chamber has been cut 3/8" to ½" deep, switch to the finisher. Continue the cutting with a series of 1/32"-1/16" increments. Remember what I said before about cleaning and lubricating a reamer after each cut? This is the perfect time not to ignore the advice.

Application of the finisher can continue until the chamber has been cut to 0.030-0.050 from the finished depth. Stop. Cease. Halt. Do not go deeper. Not right now. Not yet. See the drawing illustrating removing the sharp edge at the chamber entrance. Radius the sharp edges of the chamber accordingly. Reenact the brush-off/baptism and insert

The square object on the extreme end of the reamer is a caliber-specific pilot. Note how it has contacted the bore, giving a major assist to maintaining concentricity. the finisher again. Continue reaming to the final chamber depth without forgoing an additional reenactment after each and every increment has been cut. Final Cleanup Place both reamers in a container of good quality solvent. Allow to soak. Spray the chamber with solvent to dilute cutting oil residue and loosen any metal chips.

Blow the chamber and bore clear with compressed air. Wipe out the chamber with lint-free cloth The description in the illustration fully explains what it is all about. The rest of it illustrates how to perform the task described. wrapped around a wooden dowel to form an oversized cotton swab. Run a clean patch through the bore and all the way out the muzzle. If all this clean talk is boring you stiff, know that I’m understating its importance. Look at it this way. Clean and lubed reamers don’t scratch chambers.

Pilots don’t scratch bores. Metal chips left behind in any chamber work, however, do scratch bores. Enough said. Part eight in this series is next up. AG American Gunsmithing Association