For the last few weeks I have been testing the new hunting bullets from www.cavitybackbullets.com in particular their 6.8 120 MKZ. Just as the thread title says MKZ stands for maximum kill zone these bullets are designed to expand up to 2.5 times the caliber, at a very wide velocity range from 2800 fps to 1400 fps.

The MKZ bullets are solid copper monolithic bullets. As we know copper weighs less than lead, so a copper bullet the same weight and caliber must be longer than the same weight and caliber lead bullet. A longer bullet leaves less room for power in the case limiting the weight of most copper bullet designs, but the "Cavity Back" bullets as the name suggest have a cavity in the rear of the bullet. This cavity allows more room for powder, with the 6.8spc 120MKZ I was able to use the same powder charge as the 120gr SST with no powder compression.

At the time of writing this report I have taken 26 feral hogs with the 120 MKZ. While this is a small sample the results have been positive, and consistent enough for me to feel comfortable releasing this report. Ranges have been from 40 yards to 150 yards, no recovered bullets yet all completely passed through. Exit wounds all have a triangular shape and average between 1/2 inch to 1 inch in diameter, producing massive amounts of blood loss. Some copper bullets tested in the past did very well when hitting solid mass like muscle and bone but would zip right through if you missed the mark and hit soft tissue farther back back. So far the MKZ has not experienced this problem and seems to expand and transfer energy to the target regardless of hitting soft or solid tissues, knocking down running hogs even with bad shot placement center gut shots.

Here are a few graphic pics below showing the typical MKZ exit wound.

Thanks for the info looks like a good hog killing bullet. Are your results with this new bullet better than with 120 SSTs?

Edit:

Looks like 2 cannelures or pressure bands cut into the bullet? Did CBB share any information relative to pressure sensitivity for hand loading?

Velocity !?!?!

Did they send you loaded ammo or did you load these up?

Thanks

Nice shooting, looks like the bullet put 'em down quite well. Not sure about how the cavity allows the use of more powder though, unless the copper that's 'removed' to make the cavity is added to the nose of the bullet, making it longer overall?

I recived loaded and non loaded, for the bullets I loaded my standard 120gr sst load worked great as you can see. The point of impact was higher with these due to the higher BC.

This is the only info I have from cbb.

120 Grain MKZ .277/6.8
Ballistic Coefficient .423 G1
Length 1.21 inches, 30.73mm
Opening speed range 2800 feet per second to 1400 feet per second.
Benefits of Cavity Back Bullets (short version)
Cavity Back Technology
Hybrid Ogive
Match Grade Performance
Consistent Projectile Construction
Top Grade Projectile Copper
Caliber Specific Designs
Increased Velocities
Lower Engraving Friction
Maximum Weight Retention
Easily Tunable Projectiles
Higher Expansion Rate Than Other Copper Projectiles (up to 2.5 times caliber)
Higher Ballistic Coefficient
Benefits of the Cavity Back system (long winded versionJ)
After much testing as well as consulting with industry professionals these are the benefits of the Cavity Back in small cartridges in gas operated firearms. Many of these benefits also equate to projectiles of any caliber with the Cavity Back system.

1. The cavity in the rear of the projectile allows for more room for a larger powder charge than a projectile with a typical flat, boat-tail or rebated boat-tail design. The cavity effectively increases the capacity of the cartridge case by typically .5 to 1.5 grains of powder weight determined by powder density and caliber diameter.

2. By increasing effective case capacity the cavity allows the cartridge to “breathe” better. Resulting in a slightly cooler burn and slightly less violent activity inside the cartridge case during propellant ignition. Also allowing for more powder before compression.

3. The area inside the cavity actually has pressure inside it just as an even pressure acts on the outside of the boat-tail. As the projectile exits the muzzle the gases are forcing their way past the projectile and into the air. Some call this “blow by blast”. It is fairly well known that these gases then pass the projectile and envelope it during the first part of its flight out of the barrel. It is known that a rebated boat-tail or a small conical area in the base of the projectile or a combination of the two can cause a projectile to be more accurate. It is thought this is caused by escaping gases, that typically cause turbulence to the projectile, are directed in a slightly wider area and do not envelope the projectile to the same degree as a flat based or non-rebated boat-tail. With the cavity back the gases are forced even more outward as the projectile exits the muzzle inhibiting the turbulence and allowing the projectile to “go to sleep” quicker resulting in a more accurate projectile.

4. A longer projectile for a given weight has more external surface area allowing the spin and air movement over the projectile to help stabilize it better, provided the twist rate is high enough. Lengthening the projectile allows for a higher ballistic coefficient than a projectile of the same weight of the same composition and shape.

5. Due to its particular shape, the bullet has its center of mass behind its center of pressure. When the bullet is in flight, the center of pressure always positions itself in the direction of flight, that is, with the tail pointed forward, pivoting on the point of pressure. If the bullet is not stabilized, these two forces acting together will cause the bullet to tumble. We can consider the distance between the center of mass and the center of pressure as a lever. The longer the “lever” is, the higher the destabilizing force it causes. Longer bullets, and especially bullet shaped with long ogives, have longer “levers” and thus are the most unstable. The Cavity Back shifts the center of gravity or center of mass forward decreasing the length of the “lever”. Enhancing the Dynamic Stability of the projectile.

Cavity Back Technologies LLC

The bullet is longer overall but because of the cavity instead of a flat base bullet you do not compress the charge. At least thats how it was explained to me.

120gr sst is hard to beat, these show very good potential but only 26 hogs down so far we will see after a couple hundred.