What is Better, Stainless or Chrome-Moly Steel?
Over 90% of high-grade match barrels are made from Stainless Steel. Stainless is easier to machine because it is slightly softer. It is also easier to apply a fine, hand-lapped finish to a stainless bore. That said, chrome-moly barrels can be just as accurate, when made correctly, and there is evidence a chrome-moly barrel will hold its accuracy longer than a stainless barrel.
What is the Best Barrel Length?
Different shooters have their preferences, but here are some general guidelines:
100/200 yd 6mm Benchrest Gun: Use a short, 20"-24" barrel. 22" is ideal, but you may want to start with 24" so the barrel can be set back as the throat wears, or if you want to convert to a different caliber (i.e. from 6BR to 6PPC)
300m to 600m: A variety of lengths will work here, but you will probably be shooting heavier bullets, with a slower-burning powder, so you want a longer barrel that will give you more velocity. We recommend 26"-28". However, barrels as short as 24" do just fine at 600 yards with the right bullet.
600m and Beyond: Go with at least 28". A 30" length tube may be even better, but with some powder/bullet combinations, you may actually get less velocity with a barrel much longer than 29". With a standard 6BR case, 28" is probably long enough, while a 6BR Improved case can give a little more velocity with a 30". But keep in mind shorter barrels will be stiffer, if they are the same contour.
How Much More Velocity Will I Get with a Longer Barrel?
Going from 20" to 24" can increase velocities up to 160fps (40fps per added inch), depending on the rifling. After that, expect another 25-30fps extra velocity for each added inch up to about 28". Beyond that, you'll probably get a little extra speed, especially with 6BR Improved cases. We recently completed a barrel velocity test using a rail-gun. A Krieger 6mm barrel chambered for a standard 6BR was cut down from 33" to 28" in one-inch increments. The Average Velocity at 33" was 40 fps higher than at 28". The Average Velocities showed a pretty steady increase of 8 fps per inch past 28". For example the Average Velocity at 30" was 16 fps higher than at 28". Based on this study, you're not going to gain much by going from 28" to 30". And world-record-holder Richard Schatz is getting 3025fps with his 6 Dasher using a 26" Hart barrel. So arguably, 26" is long enough, at least for the Improved cases. For maximum speed, 30" is a useful limit, but remember that this adds weight to the gun and you'll be sacrificing barrel stiffness.
Are Shorter Barrels More Accurate?
As a general rule, the answer is yes. A shorter barrel will be stiffer, pound for pound, since you can run a thicker contour (diameter) with the same weight. As you increase diameter, barrel rigidity rises to the 4th power of the increase. But if you lengthen a barrel, stiffness declines in proportion to the cube of the length. So a barrel that is just a few inches longer and a bit thinner can be half as rigid as a 20" max contour barrel (More details). The added stiffness of fat 20-22" BR barrels raises barrel harmonic frequency to the point that barrel vibration becomes a non-issue (provided the bedded action is rigid as well). Common sense tells us that it is easier to make a shorter piece of steel perfectly straight, and with less bore length to drill, there is less chance of a flaw in a shorter barrel. Benchrest competition proves that short barrels, in the 20-22" range, give maximum short-range accuracy in 6mm, assuming you use a scope. For a gun with iron sights, longer barrels offer increased sight radius which helps the shooter aim more precisely. And don't think that a 26" or 28" barrel can't be very accurate. We've seen 28" barrels deliver 5-shot groups in the "ones" at 100 yards.
What Contour (Diameter) Should I Use?
For a gun to use for both short-range and 600-yard Benchrest competition we would use a Max Heavy Varmint taper or something very similar. This will be 1.250" at the receiver running straight for 5" (measured from bolt face), then tapering in a straight line to about .92" at the muzzle, finished at 27"-28". For 1000-yard competition, you can run a heavier taper such as the MTU, as long as the receiver or a barrel-block provides sufficient support. For point-blank shooting, if you are not planning to compete in NBRSA or IBS registered matches, we would consider a near-full contour, running 21" to 23".
What Barrel Twist Should I Use?
The most versatile barrel twist rate is 1:8". This will shoot everything from 62gr FB bullets to 107 VLDs with great accuracy. If you shoot mostly at 100-200 yards, a 1:14 twist will deliver 60-70gr match bullets with unrivaled accuracy. Take-off 1:14 6PPC barrels rechambered to 6BR work great at low cost. For shooting out to 600 yards, in calm conditions, you may get best accuracy with custom 75-85gr FB bullets. These work best in a 1:12 twist tube. A 12-twist is perfect for varminting with the 75-grain V-max and the Berger 80gr MEF. Our initial testing shows the 1:10 twist to be very effective with the new low-drag 85-88gr FB bullets, and 90gr boat-tails. The 1:10 twist is a great choice for varminting and Egg Shoots because you can run the 87gr Hornady V-Max and shoot Lapua's very accurate 90gr factory-loaded ammo. If you need a barrel to shoot both light and heavy bullets, the best choice is still a 1:8. For the 115gr DTAC bullet, 1:8 will stabilize in most conditions, but 1:7 is a better bet.
Does Twist Rate Make a Difference in Velocity?
Yes. Our tests show that, with the 80-90gr bullets, a 1:10 or 1:12 barrel will give you as much as 80fps more velocity than a 1:8 barrel, shooting the exact same loads. Fast twist (1:8) barrels have more drag and friction, which can slow the bullet down. Ideally you want to use the slowest twist rate possible that will stabilize the bullet you choose to shoot. For a dedicated "point-blank" 100/200 yard Benchrest gun, you want a twist rate from 1:13 to 1:15. But if you want to shoot both light (60-80gr) and heavy (100gr+) bullets, stick with a 1:8.
What Are the Different Kinds of Rifling Available?
There are three kinds of rifling offered by "boutique" barrel-makers such as Broughton, Hart, Krieger, and Lilja. First you have push-buttoning. This involves pushing a mandrel slowly through a pre-drilled bore. Hart barrels are push-buttoned. Second you have pull-buttoning. The procedure is similar but the button is pulled through the bore. Makers like Shilen, Lilja and Schneider use this pull-button method as they believe it produces better results. Both methods of button rifling can be used to produce either conventional square lands or profiled lands, such as found on Broughton's 5C barrels and Scheider's P5 Polygon Form Barrels.
The third option is cut rifling, a completely different system. Cut rifling is done by Border Barrels, Jeff Lawrence, Krieger, Obermeyer, and Rock Creek. Among these barrel makers, Border, Obermeyer and Rock Creek offer the Obermeyer 5R land profile, which tapers the land on one side. Claimed 5R benefits are reduced fouling, better gas sealing, and higher velocities. We do think that cut-rifled barrels, in general, tend to exhibit long useful life. Metal stress is minimized with cut-rifling, and this method, when done right, produces bores which are very uniform and concentric.
In addition to the methods above, big companies offer hammer-forged barrels. These are made by large companies such as FN, Remington, Ruger and SigArms. Hammer-forged barrels are first drilled, then the rifling is formed by pounding the external steel around a mandrel. This mandrel can impart a conventional rifling form, a polygonal form, or a tapered lands form. For a very complete discussion of barrel manufacturing techniques, click here. This is a must-read.
Which is Better, Button Rifling or Cut Rifling?
There is no clearly superior form of rifling. Check the results from major benchrest matches and you will see both cut-rifled Kriegers, and button-rifled Harts, Liljas, and Shilens among the trophy-winners. David Tubb has dominated cross-course and high-power shooting with Schneider pull-buttoned barrels, but Kriegers are favored by many Palma shooters and members of the USA F-class team. Button rifling can produce a very smooth interior finish, and the majority of winning 6PPC barrels are buttoned. On the other hand, many shooters believe cut-rifled barrels last a bit longer. By the nature of the manufacturing process, cut-rifling puts fewer stresses in the steel and twist rate is more likely to be uniform. Additionally, a cut-rifled barrel can be fluted before the bore is rifled. On buttoned barrels, fluting must be done after the bore is rifled and stress-relieved, so there's a chance stresses from profiling/fluting can alter the bore. The only possible issues we've heard with cut-rifled barrels, particularly Kriegers, is that the high, sharp lands can be tough on 6.5mm J4 jacketed bullets, such as the Clinch Rivers and JLKs, when they are driven above 2950fps in an 8-twist barrel.Full Article on Barrel Rifling.
What Is the Best Number of Grooves?
Barrel-makers report that, as long as the ratio of lands to grooves is relatively constant, there is no demonstrable difference in accuracy among 3-,4-,5-,6- and 8-groove barrel designs. Krieger has told us "There isn't any advantage to the shooter. Assuming the ratio of the surface area is kept the same, the number of grooves should not have any effect. Barrel makers use different numbers of grooves for ease of manufacturing and ... marketing hype." That said, in our experience, 8-groove barrels are a little slower, and may foul a bit more quickly because there are more edges to cut into the bullet's jacket and to trap powder residue. We see no reason not to specify a 4-groove barrel if that is your preference. Moreover, IBS Hunter Champion Al Nyhus and others have had great success with Lilja 3-groove barrels. Al believes the 3-groove design cleans up more quickly and yields a bit more velocity. Famed gunsmith and wildcatter P.O. Ackley believed that, all things considered, a properly-made 3-groove barrel is optimal for most common calibers. Ackley believed 3-groove profiles can deliver higher velocities with less fouling and no significant reduction in accuracy. In the months ahead, 6mmBR.com plans to do a comparison test of various barrel formats.
Will Using Moly Bullets Extend Barrel Life?
Probably. Though this is controversial, studies by European barrel-makers indicate that use of moly bullets from the start may extend a barrel's useful life up to 50% compared to a barrel that used "naked" bullets exclusively. That said, the part of a barrel that wears out first is the throat. Throat wear is mostly caused by heat and pressure. By backing down your charges somewhat, you can extend your barrel life significantly, and avoid some problems associated with moly. 1000-yd shooters have turned away from moly because of unexplained flyers, and some people complain that moly buildup in a bore is worse than copper because moly is quite difficult to remove without abrasive bore cleaners. Still, we think moly makes sense for rapid-fire match shooters who may shoot 40-60 rounds in a relay without the opportunity to clean.
What Kind of Barrel Will Foul the Least?
Fouling is more a symptom of a poorly finished barrel than it is associated with one particular kind of rifling vs. another. When properly machined with sharp cutters, and carefully lapped, both cut-rifled barrels and button-rifled barrels should foul very little. However, there is good evidence that canted-land barrels or polygon barrels may foul least of all, even while delivering enhanced velocities. This is because the edges of the lands are slightly rounded or tapered. In theory, profiled lands shave less copper from bullet jackets and form a better gas seal behind the bullet.
Is Fluting a Good Idea? Does it Make a Barrel Stiffer?
There are many popular misconceptions regarding fluted barrels. First let us say fluting is done primarily for weight reduction and esthetic reasons. It is generally not a great idea to flute a match barrel unless this is necessary to "make weight" with a given barrel length and contour. If you are sure you want fluting, it is best to start with a cut-rifled barrel because the fluting can be done by the barrel-maker before the bore rifling is cut; therefore there is no chance that fluting can harm bore uniformity. By contrast, a button-rifled barrel can be fluted only after it has been rifled and stress-relieved.
Fluting and Barrel Heating: Many people ask "Won't a fluted barrel cool better?" The answer is maybe. Depending on the shape and depth of the flutes, fluting can increase the overall surface area of the barrel. Provided there is good airflow around the barrel, this can enhance the barrel's ability to transfer heat. However, bead blasting a non-fluted barrel can work just as well. Moreover, you must remember that fluting reduces total barrel mass. A metal object of lesser mass will heat up faster than one of greater mass. So, with fluting, your barrel may shed heat a bit faster, but it may also heat up more quickly in the first place.
Fluting and Barrel Stiffness: Fluting does not make a barrel stiffer. However, the weight reduction allowed by fluting permits you to start with a heavier barrel contour and end up at the same weight as an un-fluted barrel of a smaller diameter contour. This may result in slightly better rigidity, but extra stiffness is not something you can count on. Look at winning guns on the firing line at short- and long-range benchrest matches. Only a small fraction of the barrels will be fluted, and usually those started out as very heavy or very long blanks and the fluting was needed to meet weight limits or to reduce the load on the receiver. A better way to hang an extremely thick, heavy barrel on a long-range benchrest gun is to use a bedding block. This supports the barrel immediately in front of the receiver for five to eight inches.
What is the Best Way to Break-in a Barrel?
There are three schools of thought on barrel break-in. First, famed barrel-maker Gail McMillan believed "less is more". Simply shoot five shots, clean, shoot another five shots, clean, and then clean every 5-10 shots or so over the life of the barrel. He argued that the "one-shot, one-clean" ritual was a gimmick devised by barrel makers to wear out barrels more quickly so they can sell more product. He rightly points out that every shot down the tube just reduces your barrel's maximum accuracy life.
The second school of thought, with Krieger in this camp, suggests to shoot and clean after every shot for 5 shots, then again after every 3 shots, until fouling is not noticeable: "Initially you should perform the shoot-one-shot-and-clean cycle for five cycles. If fouling hasn't reduced, fire five more cycles and so on until fouling begins to drop off. At that point shoot three shots before cleaning and observe. If fouling is reduced, fire five shots before cleaning." Full Article.
The third and last school of thought says to clean aggressively after every shot for a dozen shots or more, and to use an abrasive lapping compound such as JB after each of the first few shots. The idea is that this will "polish" up the throat to reduce fouling and enhance velocity. Along with bore paste, you can fire-lap the bore using bullets impregnated with fine abrasives. This is done most easily with the Tubb Final Finish system which contains bullets with five different grit levels. So, what procedure should you follow? We think Gale McMillan is probably right, but he was talking about fine custom barrels that are already hand-lapped to a mirror finish. If your barrel is rough to start out with, the other methods have some merit. We would not use Final Finish on a hand-lapped custom barrel however.