Hendon Publishing - Article Archive Details
Federal’s TruBall™ Rifled Slug
Written by Tom Burczynski
Federal Cartridge’s TruBall™ rifled slug load is specifically designed to enhance accuracy in smoothbore shotguns. It bridges the accuracy gulf between rifled barrel accuracy and smoothbore accuracy. TruBall ammunition utilizes a rifled Foster Slug as one of its three essential components, but the similarity between it and conventional Foster slug loads ends there.
Over the years, many attempts have been made to increase the accuracy of the original Foster slug. These efforts resulted in heavy slugs, light slugs, rifled slugs, conical slugs, truncated cone slugs, shouldered slugs, finned slugs, and various hybrids of these. However, none of these concepts improved accuracy to any meaningful degree. In some cases, accuracy suffered even further at the expense of a marginal gain in terminal performance.
Depending on the barrel length and choke, and even the particular shotgun in use, Foster slug accuracy ranged from poor to atrocious. Five-shot groups almost always contained a couple of mysterious flyers, which further increased an inherently wide dispersion.
The main problem with conventional Foster Slug loads has to do with excessive clearance between the outside diameter (OD) of the slug and the inside diameter (ID) of the shotgun bore. The lead skirt in the undersize lead slug can’t expand (obdurate) enough upon firing to fill the bore and is therefore incapable of coaxial alignment within the barrel. What little obturation occurs is non-concentric. The wad and slug are misaligned with one another from the very start.
Upon firing, the slug’s skirt is shortened and its base is distorted, asymmetrically. Instead of fully obturating, the skirt wall thickens and much of the lead flows inwardly. With conventional slugs, skirt deformation occurs more on one side than the other. The bottom line is the excessive clearance results in such undersize slugs haphazardly hugging one side of the barrel or the other and ultimately exiting the muzzle in a totally random manner from shot to shot.
This random orientation at muzzle exit results in unpredictable and unacceptable on-target dispersion, which is oftentimes disproportionately amplified as distance increases. The obturation related accuracy problem exists whether the slug sits atop a conventional wad or plastic buffer.
Centering the slug within the bore by creating a tight, post-ignition fit via “forced obturation” greatly enhances accuracy. The TruBall design achieves the aggressive obturation necessary with utmost mechanical efficiency, which is why it is able to deliver heretofore unattainable smoothbore accuracy.
The TruBall system consists of three key components inside the hull: 1) a rifled Foster Slug, 2) a solid Polypropylene ball and 3) a High Density Polyethylene wad with a centralized cavity in its leading end and a concave cavity in its base. The plastic wad ues a series of ribs that collapse upon firing, softening recoil.
With the exception of its new, hardened surface recently developed in-house at Federal, the Foster slug used in this load is the same pure lead rifled slug used for years in their conventional slug loads.
The plastic ball is the heart of the design and is the vital link which centers the fore and aft components. The plastic ball is perfectly round, whereas the slug’s base cavity is oval in shape since the wall thickens and curves inwardly as it extends toward the nose. The diameter of the plastic ball is such that, prior to firing, it extends only partway into the slug’s base cavity. The plastic wad’s shallow cylindrical cavity accepts the exposed portion of the plastic ball. Unlike conventional slug loads, this triadic arrangement force-centers the slug and wad both prior to and after firing.
Upon firing, several things occur in rapid sequence. Expanding gasses radially expand the wad’s concave base. This provides a tight, self-centering, “aft” fit. The wad’s ribs collapse and expand radially, providing a tight central fit. The front portion of the wad forcibly drives the plastic ball into the slug’s base cavity, radially expanding (obturating) the lead skirt within the bore in an extremely uniform manner. This provides a tight, self-centering “fore” fit.
The flat face of the wad mates with the flat base of the slug, which assists the plastic ball in creating an even more uniform obturation during axial compression. At the moment of exit, expanding gasses force the rear of the wad to flare outwardly. This creates momentary drag in flight, which forces a clean separation of components, an additional key to accuracy.
Unlike a traditional Foster Slug load, the plastic ball in the TruBall system forces the lead skirt outwardly rather than allowing it to flow inwardly. In fact, the TruBall slug has no choice in the matter since the solid plastic ball almost completely fills its base cavity, providing internal opposition and thus preventing nearly all inward flow. There’s only one direction in which the bulk of the lead can move and that’s outwardly. The TruBall Slug grows in diameter, concentrically, and becomes a ‘custom fit’, regardless of internal barrel dimensions. During this process, the plastic ball is locked in place.
During passage through the barrel, the tightly compressed components act as a single, temporarily welded unit. The length of the component train (i.e., a transient projectile) is an important accuracy factor. A long, tight-fitting projectile will always maintain a more coaxially aligned exit than will a short, undersize one. The difference in accuracy between the two is significant.
The Polypropylene ball, which is harder and tougher than lead, is locked in place during free flight. Its presence provides internal ‘solidity’ and typically remains intact and anchored during the slug’s initial penetration of hard barriers such as sheet steel. This added rigidity provides an important tactical advantage over conventional hollow-base slugs. The TruBall slug tends to resist over-expansion when hard barriers are involved, and this adds to its ability to penetrate.
Federal currently offers three basic TruBall products, two in 12 gauge and one in 20 gauge. All loads are intended for use in 2-3/4 inch and 3-inch chambers. One of the 12 gauge offerings is a full-power, 1 ounce load at 1600 fps. The other is a 1 ounce, low recoil load at 1,300 fps, which generates about a third less recoil. TruBall ammunition is color-coded. The Law Enforcement-only 12 gauge loads for law enforcement and government use have blue hulls and real brass heads. TruBall ammunition sold commercially sports a maroon hull color.
TruBall Accuracy Results
Accuracy testing at Federal involved a fixed mount system with a 20-inch Remington 870 barrel. The range is 50 yards. The accuracy, of course, varies by the choke. The average of six, 5-shot groups with the full-power, TruBall ammo was Cylinder Bore: 2.8-inch, Improved Cylinder: 2.6-inch, Modified Choke: 3.3-inch, and Full Choke: 3.5-inch.
Federal’s in-house tests reveal a significant difference in accuracy between Federal TruBall ammunition and its own standard rifled slug loads when fired from a fixed mount at 50 yards. The average group sizes for both the full-power and low recoil TruBall loads were about half the standard Federal slug loads.
Bench Rest Accuracy
We fired the TruBall ammo from an off-the-shelf Remington 870 (Cylinder Bore, 20-inch barrel) with 1.5-5X Leupold scope to verify the Federal fixed mount results. Ten 5-shot, 50-yard groups were fired using the full-power, 12 gauge TruBall load. The average of all ten, 5-shot groups was 2.3-inches.
TruBall slugs provide plenty of penetration through hard barriers. For example, they easily penetrate two pieces of 20 gauge sheet steel and continue to penetrate over 17 inches of lightly-clothed 10% ballistic gelatin, while remaining intact. Typical expansion in gelatin consistently exceeds one inch.
Federal's patent pending TruBall™ slug system is groundbreaking technology, which will forever change the way we view smoothbore shotgun accuracy.
Tom Burczynski has been involved in ballistic research and development, patent development, and ballistic testing since 1975. His primary area of expertise is bullet design. Some of the more notable bullet designes that Burczynski has developed are: Hydra-Shok™, Starfire™, Quik-Shok™, EFMJ™, and Tunnel-Point™. He may be reached at email@example.com.
Published in Tactical Response, Jan/Feb 2006
Rating : 9.1
Related CompaniesFederal Cartridge
Related ProductsAmmunitionFederal Cartridges TruBallLong gunsRifled SlugsRiflesSmoothbore Shotguns
Click to enlarge images.