Rifle Barrel Accuracy

As the gunsmith/rifleman takes on the role of machinist and ballistic technician in the extreme accuracy arena, his or her every skill will be tested. In this treatise I will delve into the selection, installation, and evaluation of two match grade rifle barrels, both chambered for the same cartridge. Each will be used as test barrels on near-identical, highly accurate Model 40X Remington switch-barrel rifles.

Following the installation of these two match grade barrels, I will perform comparative tests on them, carefully analyzing performance of each one. Cartridge Selection In its own right, the cartridge becomes the nucleus with many other key points evolving around it. Obviously a cartridge must fit one’s needs as it relates directly to the chosen barrel and should involve careful consideration in its selection. While each cartridge is designed for a purpose, some have an inherent accuracy potential over others.

Typically the gunsmith builds a rifle and turns it back to a customer for testing and use. My objective here will be assembling, testing, and realizing the quality potential of the chosen cartridge and all the ancillary parts and equipment. For this plan I have selected the 6.5x47mm Lapua cartridge for the two test rifles, a cartridge which I will describe in some detail for its merits.

The 6.5x47mm Lapua cartridge was developed in 2005 by an ammunition maker Lapua, Nammo, Inc. (nammo.com, lapua.com, for long range competition. It was quickly recognized as a cartridge with superior ballistics, including excellent accuracy, low recoil, and long barrel life. That’s making quite a claim considering 6.5mm caliber cartridges have been treated as a sort of stepchild by the American shooting industry for many years.

Lapua offers strong and uniform cases for the 6.5×47 and I can attest to the quality as I have worked with most of them for many years. This information should be recorded for future reference and is required whenever a barrel is sent back for inspection. Below center: Perfect coaxial alignment is required originating at true center when machining rifle barrels for extreme precision and accuracy.

Here a Krieger match grade barrel is being set up in a conventional lathe using a special ball bearing center rest designed by author. One of the two barrels chosen for this project was made by Krieger Barrels (kriegerbarrels.com, Krieger barrels are rifled via a highly precision, single-point, cutrifled process in calibers .20 through four bore since 1982 when John Krieger founded the company. Barrels are lapped after reaming and then hand lapped again after rifling.

As with most barrel makers, they offer a rifling twist rate to fit the needs of the shooter which is of utmost importance in selecting a barrel. If you error here it’s best to be on the faster-twist side. An under-stabilized bullet is a sad waste of time. For this particular 6.5×47 Lapua chamber I had in mind, I went with an in-stock, four groove, 416 stainless target barrel. Finished length is 26 inches measuring 0.930" at the muzzle with a 1:8 twist and a 5 lb.

Above and center: While remaining in-line and perfectly centered in the center rest, the chamber is reamed. Final reaming to correct cartridge headspace is accomplished by hand. 5 oz. total weight. Bore diameter is 0.256 with 0.264 groove diameter and a land depth of 0.004. The barrel had a 6 x 1/4" fluting which was already performed on this in-stock barrel. This would tend to reduce the overall barrel weight a bit, but would not likely affect accuracy, nor improve it.

At least one major barrel maker stipulates that fluting voids the warranty of their barrels. In my own experience, fluting has produced no remarkable difference in accuracy, for better or worse. The number of lands and grooves in a barrel is perhaps a moot point relative to accuracy. I have used from three to eight groove barrels in a given caliber with no determinable difference in accuracy.

Below and center: As a means of micro lapping the receiver/barrel joint, author uses J-B Bore Bright—a mild abrasive—between lightly tightened barrel-to-receiver union. A zero tolerance fit is achieved in this way. Accuracy problems can often be traced back to a faulty barrel joint. The second 6.5x47mm Lapua barrel used is by Criterion Barrels (criterionbarrels.com, Criterion Barrels make precision button-rifled, hand-lapped barrels in all standard calibers and rifling twists.

Though this is my first experience installing a Criterion barrel on my target/test rifles, I have had former experience with them. While at a Weatherby Writer’s Conference we actually got to assemble the Weatherby Mark Vsingle-shot Super Varmint Master rifles and barrels from Criterion were used. Those rifles used and tested in .223 Remington, .22-250 Remington, and .243 Winchester all shot very well. I still own and use the Weatherby Mark Vas one of my reliable switchbarrel rifles.

The 6.5mm (.264") Criterion barrel used in this evaluation is a 1:8 twist button-rifled, 416 stainless, six-groove, 27", 5 lb. 10 oz. barrel measuring 0.825" at the muzzle. Bore diameter is 0.2555" with a groove diameter of 0.2638" and land depth of 0.00415". Both barrels are chambered for the same cartridge, their 1:8 twists will stabilize all the better bullets up through 142 grains, and were installed with the same precision standards and equipment on well-proven rifles.

Barrel fitting and chambering went well as I machined each of them to Model 40X Remington switch-barrel rifles, each pillar-bedded into factory stocks. Special emphasis is always directed to the barrel/receiver joint which must be flawless. Any discrepancies here will show up to some degree as erratic performance. Accuracy discrepancies in the sub quarter-minute-of-angle range can often be traced back to the crucial barrel-to-receiver joint with the cause thought to be elsewhere.

I use a conventional lathe for all my barrel work. Barrels are aligned

in a center rest of my own design with ball bearing tipped jaws. The barrel doesn’t leave the center rest until the tenon, shoulder, bolt head recess, threading, and chamber reaming are all completed. This involves a few hours of precise lathe work which I never rush. I used a Dave Manson precision reamer (mansonreamers. com, with 0.2555" removable pilot.

This Manson reamer cuts a fairly tight neck so I outside turned the Lapua case neck walls from the normal 0.015" to 0.013", which allowed about 0.002" clearance on each side of a loaded round. I always cut a short chamber about to the datum line on the cut-off inch of barrel muzzle as a seating depth gauge for precise bullet seating. It also comes in handy in monitoring case neck wall thickness in avoiding thick neck walls on repeated firing. I really miss this little aid on those rifles I don’t have one.

Barrel Break-in and Testing In the evaluative process a rifle barrel must be properly broken-in. Most barrel makers lay claim to their own special break-in method. I believe Krieger describes this best. Quoting their Break-in and Cleaning Instructions, "Very little is done in the bore during break-in, but the throat is a different story. When the bullet is forced into the throat, copper dust is released into the gas as plasma. The copper dust is vaporized and carried down the bore where it is deposited.

This makes it appear as if the fouling source is the bore, when it is actually, for the most part, in the new throat." Over the years of breaking in bores I had noticed such copper fouling accumulating more in the muzzle area and a bit farther down. I then began polishing the bore throat with a lap of 3M 600 U. S. Mesh (15 micron grade) polishing paper immediately after cutting anew chamber. This has been an expedient for me in bore break-in that results in most excellent accuracy.

As it comes time for me to test my work, a task normally performed by the owner of a newly barreled rifle, I have a distinct advantage as a gunsmith/rifleman because my shop has handloading equipment and a range just outside. I can obviate shooting conditions and don’t need to pack up my things and head for a distant range to test them. With a supply of 6.5×47 Lapua cases prepped and necessary components available, I looked forward to the testing of both barrels.

Few riflemen relish bore cleaning or the bore break-in process, but it must be done. I laboriously follow my shoot-and-clean routine for as many five-shot groups as needed as I Far All burrs and imperfections must be removed here. Around head brass screw and a mild abrasive like J-B Bore Cleaning Compound rotated at the bore mouth area perfect lapping compound. These two barrels will be carefully tested together on comparable switch-barrel rifles of proven accuracy.

Bottom 5×47 Lapua cartridge, ready to be tested in an accuracy research project. closely monitor the bore for ominous sign of copper fouling. The number of required break-in shots will vary markedly as the bore is broken in and totally depends on each individual bore. With my leade-lapping process I can typically make an early assessment of barrel accuracy potential even at this early stage. Once into the post break-in regimen, I stayed with my formulated plan.

This included a few medium weight bullets in the 107 through 123 grains, and then longer, heavier bullets in the 130 through 142 grain range. As good omens go, the shootclean process was a precursor of good things to happen. My 50-yard groups hovered in the quarter-minute range with a number of good bullets. Sign of copper accumulation with each barrel was virtually absent, whereupon I moved on with some testing with medium weight bullets in the 108 to 123 grain weight.

In my experience those bores that tenaciously accumulate large amounts of copper fouling will be less accurate in the long haul, requiring a more aggressive cleaning regimen. Using identical loads in both barrels, sev-

As barrels are being tested for accuracy, handloads must be flawless. In this limited test, the Krieger barrel shot 0.109" and 0.222" with 123 grain Lapua bullets. This level of accuracy would please the most discriminate shooter. 5×47 Lapua cartridge. Upper row is the Krieger, bottom row is the Criterion. These three earlier groups with each rifle using Berger 120 grain bullets showed excellent accuracy.

The Krieger barrel averaged 0.337" and the Criterion averaged 0.393". eral 120-123 grain bullets shot very well. With these, the Krieger barrel group averaged 0.280 MOA and the Criterion at 0.397 MOA. I then went to six proven, heavier bullets in the 136 grain to 142 grain range, shooting two five-shot groups with each bullet in each barrel for a total of 24 additional groups.

In the final analysis, I believe these to be the most valid and meaningful test comparisons of two rifle barrels that I have conducted to date. Here I was testing not only two great barrels for accuracy, but the inherent precision of two barrel/receiver joints. I also must give credit where it is due to the obviously capable 6.5x47mm Lapua cartridge, bullets, and components, as well as the much worked on Model 40X Remington rifles and the sighting equipment used.

By now I have come to trust my bench rest shooting technique. As I pointed out, the loads for each barrel were as closely matched as possible in every respect. None were tweaked to further enhance accuracy once reliable loads paralleled in each barrel. As this series of targets were completed, there were no groups measuring more than 0.500 MOA. Here two groups were shot with each of six different bullets. Each respective pair of groups is identified by the barrel, bullet and individual group size.

Bullets used, shown clockwise from upper left on target, are 142 Sierra, 140 Hornady A-Max, 140 Barnes, 140 Berger, 136 Lapua and 140 Berger VLD. In this 24 group test, the Criterion barrel averaged 0.333 MOA and the Krieger barrel at 0.338 MOA. This is exemplary performance on the part of each barrel. Nearly half of the combined groups measured in the 0.2 MOA range.

As the tests were concluded on the 24 group target, using six different match grade bullets, the Criterion barrel averaged 0.333 MOA compared with the Krieger barrel average of 0.338 MOA. In the lighter bullet category the Krieger barrel had edged out the Criterion barrel 0.280 MOA to 0.397 MOA average. In the overall 38 group average, Krieger bettered Criterion by about 0.065 MOA, the mere thickness of a penny. This is most exceptional performance by each barrel with no attempts to further improve the loads.

Of course, there are few loads that can’t significantly be improved upon. As I switched to the 300 yard targets, each barrel produced several very excellent groups, a few were under quarter MOA with each barrel and different bullets. Much more testing and evaluation would ensue, but I was impressed by that which I saw thus far. Conclusion A barrel maker that could just figure out what makes a "hummer" would corner the market. The better barrels of today are far superior to any produced over the past three decades.

Conducting a corollary evaluation on such barrels as both the gunsmith and analyst is really putting one’s work under a microscope. Scores of things are tested and evaluated, including the shooter, and any of which may go awry and lead to an inconclusive result. But if we dare to take that step, there is much to be learned and understood. AG