Polygonal rifling is a barrel design where the interior of a gun barrel is shaped into a rounded polygon, typically a hexagon, instead of the traditional pattern of sharp-cut lands and grooves. Where conventional rifling looks like a gear when viewed from the end of the barrel, a polygonal bore looks more like a softly rounded hexagon or octagon. The “hills and valleys” of a polygonal barrel are gentler and less sharply defined, which changes how the bullet interacts with the barrel in several important ways.
How It Differs From Traditional Rifling
Standard rifling cuts distinct channels (grooves) into the barrel, separated by raised ridges (lands). These lands dig into the bullet’s surface as it travels down the bore, imparting spin. The contact between bullet and barrel is concentrated at these narrow, sharp-edged ridges. If you sectioned the barrel and looked straight through it, the profile would resemble a gear or sprocket.
Polygonal rifling replaces that gear shape with a smooth, slightly twisted polygon. Instead of sharp edges biting into the bullet, the entire bore surface gently guides it. The bullet still spins, because the polygon is twisted along the barrel’s length, but the transition between high and low points is gradual rather than abrupt. A comparative study published in Science Progress found that in a hexagonal barrel, each of the six sides produces a maximum penetration of just 0.158 mm into the bullet jacket at its center, with a deformation width of about 2.86 mm. The bullet deforms slightly outward between those contact zones as well, about 0.178 mm. In other words, the bullet conforms to the polygon rather than getting carved by sharp edges.
Why Manufacturers Use It
The rounded profile creates a tighter seal between the bullet and the bore. With conventional rifling, small gaps exist between the lands, allowing some propellant gas to blow past the bullet. A polygonal bore wraps more evenly around the projectile, reducing that gas escape. This tighter seal is the main reason polygonal barrels are often credited with slightly higher muzzle velocities, though the real-world difference is modest. The same Science Progress study found “no significant difference in the pressure and velocity of the shots fired in each type of gun” when comparing hexagonal and grooved barrels under controlled conditions.
The bigger practical advantage is barrel longevity. Because the bore doesn’t have sharp edges that concentrate stress and wear, polygonal barrels tend to last longer before accuracy degrades. Glock’s polygonal barrels (Gen 1 through 4) developed a strong reputation for durability. Carbon steel Glock barrels have been reported to withstand well beyond 30,000 rounds of standard pressure ammunition. By comparison, stainless barrels with conventional rifling are often rated around 15,000 rounds for higher-pressure loads and 30,000 for standard loads.
Cleaning is also somewhat simpler. Without deep, sharp-cornered grooves, copper and carbon fouling has fewer places to accumulate and cling. The smoother transitions make the bore easier to scrub out.
How Polygonal Barrels Are Made
Most polygonal barrels are produced through cold hammer forging. In this process, a mandrel shaped with the desired polygonal profile is inserted into a barrel blank, and high-speed hammers pound the steel around it from the outside. The barrel literally forms around the mandrel, creating the rifling without any cutting. This method compresses and work-hardens the steel, contributing to the barrel’s durability.
Cold hammer forging emerged in Germany before World War II and was used in the MG 42 machine gun, one of the first modern military weapons to feature polygonal rifling. The process is fast and well suited to mass production, which is part of why polygonal rifling became commercially viable. Button rifling, where a tungsten carbide die is pushed or pulled through the barrel in a single pass, can also produce polygonal profiles, though hammer forging remains the dominant method for major manufacturers.
A Brief History
The concept dates to 1853, when British engineer Joseph Whitworth experimented with twisted hexagonal cannon barrels and patented the design in 1854. Whitworth’s hexagonal bore showed impressive accuracy for its era, but the idea didn’t gain widespread military adoption. Several late 19th-century service rifles used forms of polygonal rifling, including the British Lee-Metford and the Japanese Arisaka, but the design eventually fell out of favor.
It resurfaced during World War II with the MG 42, then largely disappeared again until Heckler & Koch revived it in the 1960s for modern small arms. HK used polygonal rifling in the G3A3 battle rifle and several semi-automatic hunting rifles, proving the concept worked reliably in high-volume military and commercial firearms. Glock then brought it into the mainstream handgun market, using hexagonal polygonal rifling across its Gen 1 through Gen 4 pistols. Today, manufacturers including CZ, Kahr Arms, Walther, Magnum Research, Tanfoglio, and Israel Weapon Industries all offer firearms with polygonal bores.
The Lead Bullet Concern
One well-known caution with polygonal barrels involves shooting unjacketed lead bullets. Because the bore wraps so tightly around the projectile, soft lead tends to build up faster than it does in conventional rifling. In a traditional barrel, the grooves give fouling somewhere to sit without drastically shrinking the bore diameter. In a polygonal barrel, lead deposits can accumulate more evenly across the bore surface, gradually reducing the available space for the next bullet and potentially raising chamber pressures.
This is why Glock and other manufacturers with polygonal bores generally recommend jacketed or plated ammunition. It’s not that a single magazine of lead bullets will cause a catastrophic failure, but sustained use without thorough cleaning between sessions can create unsafe pressure levels over time. If you own a polygonal-rifled firearm and want to shoot lead, frequent bore inspections and cleaning are essential.
Glock’s Shift to Hybrid Rifling
Starting with the Gen 5 line, Glock moved away from pure polygonal rifling to what they call the “Marksman Barrel.” This design is a hybrid, combining elements of polygonal and traditional rifling to improve accuracy. The change reflects a broader trend: some manufacturers now blend rifling styles to get the durability and gas-sealing benefits of polygonal profiles with the sharper bullet engagement of conventional lands. TRIARC Systems, for example, developed a proprietary “single edge polygonal” design that merges a polygonal profile with a defined edge for their Track 2.0 barrels.
The Gen 5 Marksman barrel does appear to have a different wear profile. The FBI’s specification for replacing Glock 17M barrels (which use the Marksman design) was initially set at 3,000 rounds, later revised to 10,000 rounds. That’s still well below the round counts polygonal Glock barrels were known for, though direct comparisons are complicated by differences in the ammunition and testing standards involved.
Does It Actually Improve Accuracy?
This is the question shooters argue about most, and the honest answer is that the rifling type alone makes less difference than most people assume. Barrel quality, bore consistency, ammunition selection, and the shooter all matter more than whether the profile is polygonal or conventional. The Ballistics by the Inch project, which has conducted extensive comparative barrel testing, noted that discussions about rifling-type advantages “have largely remained anecdotal” because so many other variables affect performance.
Where polygonal rifling does offer a measurable edge is in barrel life and ease of maintenance. For a competition shooter or someone putting tens of thousands of rounds through a pistol, those advantages add up. For accuracy at typical handgun distances, the difference between a well-made polygonal barrel and a well-made conventional barrel is negligible.