First Look: BOR Lock MZ Lead Bullet

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Muzzleloading rifles have arguably changed more in the past 20 years than bolt-action centerfires have in the past 100. Every aspect of the modern in-line — from its ignition system to sights — has evolved dramatically. The same can be said for the powders and primers that power them. Bullet design, however, has changed little.


Federal Premium is changing this with its all-new Trophy Copper muzzleloader bullet. Its BOR Lock MZ system provides accuracy in a non-sabot design that is easy to load, scrubs fouling from the breech and allows consistent bullet seating.

Sabots, Conicals And Complications


The trick with muzzleloaders has always been that in order to produce high velocities and good accuracy, the bullet must fit tightly in the bore to engage the rifling and provide a seal for the gasses propelling it. The problem is you also need to push that same projectile down the barrel in the first place during loading. This is why grossly inaccurate smoothbore muskets remained the battlefield firearm of choice long after the invention of rifling — they could be reloaded quickly because the bullet didn't need to be carefully forced down a tight-fitting barrel while enemy bullets whizzed past.

In those early days, when accuracy was needed rather than volume, shooters wrapped lead round balls in a tight-fitting cloth patch — essentially a primitive sabot. The patch formed a relatively tight seal and gripped the lands and grooves of the rifling to impart spin as the bullet left the barrel. But the time and effort required to get the bullet from muzzle to breech, and the need to swab the bore between shots to remove fouling, largely kept rifles and bullets like these off the battlefield.

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Then came Claude-Etienne Minié, a French army officer who in 1847 created a bullet design that would ultimately bear his name and change firearms forever. The cone-shaped lead projectile, the Minié Ball, was built smaller than the rifle bore to ease loading, but its concave base expanded during ignition. This sealed the bore and engaged the rifling, resulting in accuracy that was unprecedented at the time.

Despite the passage of nearly 170 years, the bullets most muzzleloaders use today basically still follow one of these two principles, using either a plastic sabot or expanding base to seal the bore. And although both improve accuracy and overall performance, they also carry baggage.

One downfall is the force required to load. Because the whole purpose of a sabot is to fit tightly, that means it is also difficult to push down the bore. And it only gets harder if you fire multiple shots with an increasingly dirty barrel. Another concern from a hunting standpoint is legality. Muzzleloader regulations vary widely, and one of the biggest sticking points is bullet design, as some areas outlaw sabots or anything else that separates from the bullet.

Although legal in more areas, bullets that feature an expanding base — usually a soft plastic flange — struggle because the flange can separate from the bullet if the gun is dropped or jarred. This can result in the projectile sitting a distance down the barrel from the powder charge without the hunter's knowledge. The softness of the flange is also prone to rupturing during the shot, degrading accuracy and velocity. Such bullets are also usually made of soft lead, minimizing their terminal performance if they do hit their intended target.

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A New System

Federal Premium recently decided to address these issues and develop a truly new class of projectile in its BOR Lock MZ muzzleloader bullet.

"The time was right. We weren't going to get into the muzzleloader market with the same sort of bullet designs that have been around for decades," said Mike Holm, ammunition product line manager for Federal Premium. "Instead, we used our 90-plus years of ammunition manufacturing expertise to create something special — something that would let muzzleloaders hunt legally in more places, with better accuracy, dependability and ease. It's a true 200-yard muzzleloader bullet."

The result was the BOR Lock MZ system. Unlike sabots or belted bullets, it features a polymer cup permanently attached to the bullet base. The unfired bullet and cup are slightly smaller than the bore, but the force of ignition pushes the cup forward onto two raised bands along the bullet shank, which essentially increases the diameter of the projectile. This engages the rifling and seals the bore, optimizing velocity and accuracy.

"BOR stands for 'Bullet Obturating Ramp.' The walls of the polymer cup get pushed up and out, into the rifling," said Bryan Peterson, Federal Premium's senior product development engineer. "You get an excellent seal — and that means better ballistics and downrange performance."

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The rear of the BOR Lock cup features a hard, fiber-reinforced polymer ring that scours fouling from the breech as the bullet is pushed into place. This decreases the need to clean between shots and makes it easy to seat the bullet at the exact same depth. Because there's no bulky sabot (only the fouling-cutting ring of an unfired bullet engages the rifling) required loading force averages about half that of most sabot bullets.

"Without cleaning between shots, you quickly build up a crud layer that not only makes it difficult to load the next bullet, it can also physically prevent a bullet from being seated at the same depth as the one before. When this happens, accuracy and consistency can really start to degrade," Peterson said. "The glass fiber we've built into the back of the BOR Lock cup shaves right through this fouling."

The bullet itself is also a giant leap forward in muzzleloader technology, built around Federal Premium's Trophy Copper rifle bullet and shotgun slug.

"For the first time ever, muzzleloader hunters can get ragged-hole sorts of groups at long range, with bullet performance — the weight retention, expansion and penetration — they expect out of their centerfire ammunition," Holm said. "We've created a whole new class of bullet."

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