A Tip on Slug Performance
January 04, 2011
Remington's new AccuTip shotgun slug looks like something from a ballistic missile development program. While that may not be far from the truth, it certainly represents the next step in slug technology.
In the world of gunpowder-powered projectiles, slugs fall just behind towed artillery. They are massive; pack one hell of a wallop on both ends of a shotgun; and until recently, were just big, gnarly hunks of lead.
The chemical bonding of jacket and core is evident by the way the lead sticks to the slug petals instead of peeling off into the gelatin.
Foster slugs came along in the early 1930s and represented a moderate improvement over round balls. Though the marketing term "rifled" managed to stick over the years, the Foster slug's improved performance had more to do with the hollow base and a forward-weighted design that was inherently more stable when slung down a smooth bore and out across hill and dale. The "rifling" cast into the slug's sides might have helped impart a little spin on the projectile, but any positive effect they had other than making the slug look cool was slight at best.
The poor fellows in shotgun-only hunting areas--by some estimates upwards of 4 million whitetail hunters are limited to shotguns or muzzleloaders--knew there had to be a better way, and they begged for it. The answer was the combination of a rifled barrel and a sabot-clad slug, and that took big-game shotgun hunting to the next level. Their performance is simply astounding when compared to round balls and smooth bores. A hunter equipped with a factory shotgun and standard ammunition could reasonably expect to extend his range from 50 or 75 yards out to 150 yards. Custom guns and competent shots could make a big Midwestern whitetail nervous even beyond 200 yards.
The AccuTip and standard Remington 11-87 proved an accurate combination. Three-shot groups averaged 3.32 inches at 100 yards.
Growing up in Georgia, I never had much use for slugs and slug guns, other than as a bull-in-the-china-shop, self-defense load for my Model 870. The serious players hunted whitetails with bolt rifles chambered for something that had "____ MAG" on the headstamp, and the old-timers toted lever rifles on opening day. But to chase monster whitetails, a fellow has to expand his horizons as well as the number of states he hunts.
Last fall, I found myself sneaking down the brushy edge of a Wyoming hay field contemplating some long-distance shooting with an autoloading shotgun stoked with slugs. The state's hunters usually carry rifles, and the guides raised some eyebrows when the shotgun was uncased at the sight-in bench, but the odd equipment had a definitive purpose: serious slug testing.
REMINGTON ACCU-TIP SLUG
|Gauge ||12 |
|Length ||2 3/4 inches |
|Slug Weight ||385 grains |
|Velocity ||1,850 fps (muzzle); 1,611 fps (50 yards); 1,401 (100 yards) |
|Energy ||2,925 ft-lbs (muzzle); 2,218 ft-lbs (50 yards); 1,677 ft-lbs (100 yards) |
|Trajectory ||+2.7 inches (50 yards); +3.6 inches (100 yards); 0.0 inch (150 yards) |
|Gauge ||12 |
|Length ||3 inches |
|Slug Weight ||385 grains |
|Velocity ||1,900 fps (muzzle); 1,656 fps (50 yards); 1,439 (100 yards) |
|Energy ||3,086 ft-lbs (muzzle); 2,344 ft-lbs (50 yards); 1,771 ft-lbs (100 yards) |
|Trajectory ||+2.5 inches (50 yards); +3.4 inches (100 yards); 0.0 inch (150 yards) |
Later in the field, I had closed to within 120 yards of a big doe feeding, and my companion, Remington's Eddie Stevenson, nodded that we had crawled far enough. The Model 11-87, equipped with a fully rifled barrel and cantilever-mounted, variable Kahles KX scope, was loaded with the then-experimental Premier AccuTip bonded, sabot-clad slug.
A few weeks before the hunt, I received about 50 rounds to zero the gun and figure out a flight path at extended ranges. That long title on the box did not intrigue me nearly as much as the tip. I called Stevenson and asked if the engineers had been hanging out with the boy
s down at NASA again.
"I don't know exactly how they do it, but they make the slugs more accurate--a lot more accurate," Stevenson told me over the phone. "You'll have to talk with the engineer for an explanation. It's really cool."
"They" were a series of evenly spaced, longitudinal holes in the light-green polymer tip. The translucent plastic tip, dark green corona of the roll crimp, and shadows between gave the shotshell the aura of a ballistic missile project gone mad. The doe would have agreed wholeheartedly. I had zeroed the gun at 100 yards and held dead on as she fed broadside. Stevenson gave me an approving look after the shot as the doe collapsed at the end of a short sprint.
More than 100 rounds were fired from the bench and in the field with no malfunctions or failures to feed.
Back at the skinning shed, we pulled the hide off the doe and marveled at nearly 2-inch entry and exit holes. Over the course of the next few days, I marveled again at how consistent the slug's terminal performance appeared to be at varying ranges. With a double handful of doe tags punched and a cooler full of meat, I returned home with plenty of questions for the mad scientist that created the new AccuTip slug.
Greg Dennison, a mechanical engineer, did not build ballistic missiles in his previous career, but he did develop new and improved, large-caliber ordnance for the U.S. Navy before coming to work for Remington 14 years ago. Dennison, now a senior research engineer, designed the slug, and engineer Dave Schluckebier worked on the load development. The project took about eight months of work once the bosses at Remington decided it was time to take slugs to the next level.
"We had two or three different tip designs all that worked to accomplish the same thing," Dennison said. "Typically, a polymer tip streamlines the bullet, improving the ballistic coefficient. This tip does something different."
Just like a race car has a center of gravity, a slug has a point where the forces of air act on it, called the aerodynamic center of pressure. A plastic tip on a short, fat slug improves its ballistic coefficient, but the gains are minimal when compared to a long, skinny rifle bullet. The holes in the AccuTip are important since they interrupt the airflow and move the center of pressure to a point that is optimal for stable flight.
"By changing the center of pressure with the holes in the tip, I can optimize the effect and make the slug as accurate as possible," Dennison said. "Without the holes, a tipped slug has a higher ballistic coefficient, but it's not as stable. This slug was all about accuracy and terminal performance."
The six holes are each .075 inch in diameter and are evenly spaced. They run through the tip and vent the redirected air out of the jacket cuts below the tip. Dennison said there was a tremendous amount of research on how the slug moved through the air, since the AccuTip was going where no slug had been before.
"We did high-speed photography and shadow graphs to measure air flow over the slugs," Dennison said. "It is hard to compare other slugs to the AccuTip because no other products have these holes."
The holes are the most obvious design feature of the slug but not the most important once the slug hits a target. Just like any other bullet, the challenge with slugs is getting them to expand and deliver their energy while penetrating sufficiently to do significant damage to internal organs. If the slug were hitting the same target at the same angle and at the same speed, the engineering would be a cinch. But hunting rarely offers that kind of consistency. Like other high-tech bullets, the AccuTip solves this conundrum by utilizing a super soft core and an engineered jacket.
While the bullet's core is nothing special--just 100-percent lead--the jacket is made from cartridge brass, not a more commonly used gilding metal like copper. The jacket and core are chemically bonded together. The package has a nice boattail-like profile that further helps aerodynamic efficiency.
"To work through a wide range of impact velocities, we had to go to a tougher brass jacket and bond the core," Dennison said. "The nose cuts and soft core keep the expansion consistent at lower velocities. The bonding keeps things together if the shot is at point-blank range. The jacket is unusually thick at the base, giving the slug the additional advantage of moving the lead core up the slug body so there is more surface area for chemical bonding."
After theorizing which design would allow the slug to work at powder-burn ranges and those pushing the limits of the best slug guns, Dennison hit the lab again to test the projectile in ordnance gelatin.
"At 100 yards in 10-percent gelatin, most slugs expand to .980 inch with near 100 percent weight retention," Dennison said. "It's the jacket that really holds things together. We also found that expansion is maximized within the first 6 or 8 inches. Penetration was great. In fact, the slug always penetrated through an 18-inch gelatin block. We usually saw a minimum of 21 or 22 inches."
Dennison's lab results were replicated in Wyoming. Pass-through shots were the norm on broadside deer, and the one straight-on shot saw penetration past the 20-inch mark into the paunch, though no amount of digging produced a slug. The bonding is very effective at holding the slug together, despite massive expansion. I dug a half-dozen slugs out of the red-clay bank behind my targets at the range. Dirt and rocks are tough on a projectile, but on average, the slugs retained 97.9 percent of their weight. The tip--because of its aggressive mechanical attachment to the slug via nose cuts--was often still on the slug. It was a less-than-perfect if not anecdotal test, but it demonstrated just how tough the slug is.
Generally speaking, at .58 caliber, the AccuTip is larger in diameter than its high-performance counterparts. Other companies utilize .45-caliber projectiles, the bullets pulled from the centerfire line.
Remington ended up using its proven four-petal sabot that debuted with the Copper Solid slug. The petals open quickly when they slam into the wall of air outside the barrel and allow the slug to pull away cleanly. Dennison said separation usually occurs within 10 to 20 feet of the muzzle. A windless day at the range offered another clue as to consistency. Most of 40 sabots fired during a test session landed within a 10-foot circle about 20 feet ahead of the muzzle.
The slug sits on top of a felt wad, and that sits on top of a round, ridge
d wad Remington named the H-wad because of its cross section. The combination allows a slight amount of set-back after the propellant charge starts to burn.
A charge of slow-burning powder allows the 385-grain projectile to attain a velocity of 1,850 fps with an overall length of 23â„4 inches. This means a slug gun zeroed at 150 yards prints 2.7 inches high at 50 yards and 3.6 inches high at 100 yards. The 3-inch magnum version gets a 50-fps boost at the muzzle from the additional propellant.
The net gain of all this research and effort on the part of Remington is a round that reaches new performance plateaus in terms of accuracy and terminal performance. The Premier AccuTip is an exceptional performer and is reasonably priced when compared to other premium slug designs. It is also pretty obvious that the tip technology could be co-opted into other rifle and handgun bullets in the next few years.
Slugs have seen an exponential degree of innovation and experimentation in the past decade, and to date, the Premier AccuTip bonded slug is on the top of the heap.