The Heart of the Rifle
By Mark Ducros Stouse
The firearms industry is not known as being particularly progressive. In a market where hundred-year-old action designs still predominate, one does not expect a great deal of change in the way anything is done or made.
No where is this more true than in the hide-bound traditionalism and dedication to quality that rules most of the makers of today's custom rifle barrels.
Understanding Basic Custom Barrel Terminology
Today's custom barrel market has never been more active. There are approximately nine primary makers of first-quality custom barrels, representing a variety of production techniques: single-point hook-cut rifling, multi-point broach-cut rifling, and button rifling. While each production method is capable of turning out a very accurate barrel when properly done, all three have their die-hard adherents and critics.
Before we begin a brief discussion of rifling types, it is important to establish a short glossary of terms.
In a rifled bore, there are two dimensions: the land dimension and the groove dimension. In a rifled barrel, land are narrow, ridge-like features that run the full length of the barrel. Typically, there are six lands separated by six grooves in a modern rifle barrel, but many are made with as few as three lands and as many as ten. The purpose of the land is to grip the bullet as it travels down the bore, and impart a specified rate of spin designed to stabilize the bullet in flight. Think of the way a quarterback throws a football, and you'll get the basic idea.
In a .30 caliber barrel, for example, the land dimension gages around .300", while the groove measures close to .308". From this, one can see where some .30 caliber cartridges get their names, e.g. the .308
The second term that is important to understand is the rate of twist. Expressed in terms of the number of revolutions per inch of barrel length, the twist rate dictates what size bullets the rifle will be able to shoot accurately. For example, the most common twist rate for a .308 caliber barrel is one complete revolution every ten inches. This ratio is commonly expressed by a shorthand designation such as 1:10 or 1/10. Other barrel makers will express the twist in terms of the number of inches, e.g. "You need a .308 caliber, 10 twist."
A good simplified rule of thumb is that the
heavier and longer a bullet is, the faster the twist rate needs to be to
stabilize it in flight. For example, a 1:12 twist will stabilize .308 caliber
bullets weighing up to 165 grains, particularly if bullet velocity is
reasonably high. In order to shoot heavier .308 caliber bullets in the 170-220
grain range, you would need a 1:10 twist.
There is another little wrinkle in the issue of twist rate, and that is the interaction between twist and bullet velocity. Let's examine two .30 caliber cartridges that illustrate this relationship: the .308
To shoot a 155-grain .308 bullet accurately in the .308
Now that we've established certain basic terminology, let's take a look at the various ways that custom barrels are made.
Single-Point Hook-Cut Rifling. This is perhaps the oldest extant technology used to create a rifled bore. First developed in the 15th century armament shops surrounding
With single-point cut rifling, the craftsman selects a length of round steel bar stock, usually about 1.25 inch in diameter, for deep-hole drilling. This operation, together with the reaming operation that follows, is as important to the overall quality of the barrel as the rifling itself. In this case, the hole is drilled and reamed to a size that is slightly tighter than the land diameter for that caliber. Here's a brief but important aside: Regardless of the rifling technique used, better barrel makers typically will run a light abrasive lap through the bore to eliminate any residual reamer marks. If a barrel maker says that he doesn't lap his barrels, and you choose to use such a barrel, you should prepare yourself in advance for some fairly rough sledding in terms of bore fouling and subsequent cleaning steps. Some barrel makers still insist that lapping doesn't matter, but the facts are that it matters quite a lot. Caveat emptor.
Once the steel barrel blank is ready, it is rifled. With single-point cut rifling, a hook-like cutter literally carves out each groove, one at a time. Generally, it can take as many as 20-30 passes of the cutter to finish just one groove. Once the rifling is complete, the barrel is contoured to the customer's specification and then lapped to improve the smoothness of the bore.
Very time and labor intensive, single-point cut-rifled barrels are typically more expensive to purchase than any other barrel type, and given the production limits of the process itself, high-volume production by a single rifling machine is all but impossible. Among its clique of devotees, single-point cut-rifled barrels are considered the Rolls Royce of custom rifle barrels. Today, the major
Multi-Point Broach-Cut Rifling. This rifling process has much in common with the single-point process, but represents an attempt to speed up the rifling process by carving out all of the desired number of grooves at once. With two exceptions, today's broach-cut barrels are not made to the same quality levels as barrels produced by single-point cut rifling or button rifling. Today, manufacturers of black powder muzzle-loading rifles use much of the annual broach-cut barrel production.
After the steel barrel blank is drilled and reamed, a series of ever- larger broaches are passed down the bore, cutting all of the grooves deeper and deeper. Once the final groove dimension is established, the barrel is contoured to fit the customer's needs and either lapped or shipped to the customer as a completed piece.
Today, the major
Precision Button Rifling. During the 1950s, Remington Arms engineer Mike Walker began experimenting with a new rifling technology that would eventually become the dominant production technique for high-quality custom rifle barrels. Called "button rifling," the new technology effectively bridged the gap between the quality problems associated with high-volume hammer forging and the production problems associated low-volume, high-quality cut rifling.
Steel barrel blanks destined for button rifling must start out the same way as their single-point cut and broach-cut cousins. The blank is deep-hole drilled and reamed, usually with rebuilt, early 20th century Pratt & Whitney drilling machines. As discussed above, some makers like to run a light lap through the bore prior to rifling, and others don't.
Made from very hard carbide, the "button" in button rifling has been carefully machined with the reverse of the rifling pattern that is desired for the barrel. It is marginally larger than the hole in the barrel blank. This button is pushed through the hole under great pressure, displacing the steel into lands and grooves. In many respects, the process extrudes the rifling into the barrel, with the button acting as a moving, mini-mandrel.
As you might imagine, this process can put a lot of stress into the barrel steel. If a button-rifled blank is contoured without any prior stress relief, the release of the radial stresses resulting from the machining process will cause the bore dimension to grow radically and unevenly down the bore. Button-rifled barrel makers most often eliminate these dimensional variations by lapping the bore after contouring until the dimensions are uniform and the surface is smooth. Some, including
BlackStar, Pac-Nor and Krieger, apply cryogenic stress relief technology to their barrels to completely eliminate stresses. In addition to being the pioneer in integrating cryogenic tempering into barrel production, BlackStar is the only barrel maker to apply this important technology twice to every barrel that it makes.
Today, most of the barrels used in benchrest competition are button-rifled, proving that these barrels are capable of producing consistently high levels of accuracy. The top custom button-rifled barrel makers in the
Hammer-Forged Factory Barrels. First developed in
In hammer forging, a short piece of barrel steel is extruded along a mandrel that has the reverse of the rifling form desired for the barrel. Unlike button rifling, however, hammer forging forms the barrels around the mandrel, rather than putting rifling into a full-length piece of bar stock. Despite all of the marketing hype, however, hammer-forged barrels are rarely paragons of accuracy and performance. Laden with internal stresses, these barrels also often exhibit very rough bores, which are the result of poorly maintained production mandrels. All in all, most gunsmiths do not consider hammer-forged barrels to be good candidates for a high-quality custom rifle.
Today, you have two basic choices in barrel steel: traditional blued chrome moly steel and the more modern stainless steel. During past years, partisans for both have made a wide range of claims about their respective qualities and advantages, most of which had little basis in fact. Today, stainless is by far the most popular steel in the custom barrel category, and it is on the rise in factory barrels as well.
Obviously, blued steel delivers the more traditional look to a rifle, and many, many shooters still prefer the old-style aesthetic to the modern, racy appearance of stainless actions and barrels. I definitely fall into this category when the subject turns to high-grade, Circassian walnut-stocked hunting guns with express sights or low-power scopes. After having done the synthetic stocked, high-performance stainless rifle bit, I have returned to the warm feel of great wood, the subdued colors of fine bluing, and cartridges that are about more than just raw, pedal-to-the-metal velocity. However, I also don't take these rifles to wet, humid places, nor do I use them in competition.
With this last two considerations uppermost in our minds, we come the place where stainless is king. If you are a benchrest or high power competitor, a stainless barrel is the way to go. Generally, the primo accuracy life of a conventional 416R stainless barrel will be a bit longer that blued chrome moly. If you hunt in soggy or salty conditions, you simply have no choice -- a synthetic stocked, stainless rifle is the only way to go. While 416R stainless is an improvement over blued steel, a new 17-4 type stainless barrel steel developed by Crucible Steel and BlackStar is by far the most corrosion resistant on the market. It is called SS700, and it is more corrosion resistant and erosion resistant than any other barrel steel currently in use. After two years on the market, barrels made from SS700 have consistently demonstrated a 3X-4X extension in throat life and commensurate top-drawer accuracy.
I own several rifles with stainless barrels, and they are really super at resisting the effects of southeast
Get the Important Parts Right
Most gunsmiths and other experts agree that if the action is the soul of a gun, the barrel is its heart. Like a high-quality lens for a camera, obtaining the best possible results demands that you make no compromises in the selection of a custom rifle barrel. After surveying the options, make your final selection based on quality, reputation and value received, not the price. Purchase the very best barrel that you can afford, and have it installed by the best gunsmith that you can find.
If you don't know a quality gunsmith, ask the barrel maker for his recommendations. Don't feel constrained by geography or your buddy's recommendation of some local shade-tree machinist - some of the best custom sporting and competition rifles available today are made by professional gunsmiths working all across the country. To perform to its potential, a high-grade custom barrel must be properly installed. An off-center chamber or an inferior thread set-up can make the best barrel ever made perform like a high-priced sewer pipe. Bottom line? Don't scrimp on your custom barrel in any way. Your satisfaction with the rifle and your success in the field depend on it.
Mark Ducros Stouse