The 375 RAPTOR was designed with multiple performance objectives:
- Performance will be achieved using a maximum cartridge length of 2.800” to allow magazine length loading in short action rifles designed to support the 308 Winchester and similar cartridges.
- Performance will be achieved using currently available hunting bullets from mainstream bullet manufacturers – Speer, Nosler, Sierra, Hornady and Barnes. Performance from match bullets, not designed for hunting, will not be considered.
- The cartridge will achieve a Minimum Effective Range of 300 yards with multiple hunting bullets. The Minimum Effective Range being defined as bullets having an On Target Velocity at 300 yards greater than 1800 fps – the minimum bullet manufacturer recommended velocity requirement to insure reliable expansion.
- The cartridge will achieve a Maximum Point Blank Range greater than 200 yards with a 6-inch diameter vital zone. The Maximum Point Blank Range with a 6-inch diameter vital zone defined as:
- Maintain a trajectory with the bullet flight path being no higher than 3 inches and no lower than 3 inches from the point of aim.
- Wind drift due to a 3 mph 90 degree angle crosswind must not exceed 3 inches from the point of aim. It is generally considered that it takes a 4 mph wind for there to be any visual or physical indication of wind.
The following set of bullets met all stated objectives equaling or exceeding the listed threshold velocities using a 18-inch barrel, 2.5 inch scope height and a standard 200 yard zero:
- Sierra 250 grain Game King @ 2460 fps with a 237 yard Maximum Point Blank Range
- Hornady 250 grain GMX @ 2355 fps with a 236 yard Maximum Point Blank Range
- Nosler 260 grain Accubond @ 2300 fps with a 235 yard Maximum Point Blank Range
- Speer 270 grain BTSP @ 2355 fps with a 233 yard Maximum Point Blank Range
Looking at this set of bullets from a terminal energy perspective,
- Sierra 250 grain Game King @ 2460 fps achieves 3,359 foot pounds of muzzle energy and 1,803 foot pounds of energy at 300 yards.
- Hornady 250 grain GMX @ 2355 fps achieves 3,078 foot pounds of muzzle energy and 1,802 foot pounds of energy at 300 yards.
- Nosler 260 grain Accubond @ 2300 fps achieves 3,053 foot pounds of muzzle energy and 1,872 foot pounds of energy at 300 yards.
- Speer 270 grain BTSP @ 2355 fps achieves 3,324 foot pounds of muzzle energy and 1,944 foot pounds of energy at 300 yards.
Reviewing the data, the muzzle energy range for this set of bullets is from 3,053 to 3,359 foot pounds. On target at 300 yards, the terminal energy range is from 1,802 to 1,944 foot pounds which is impressive considering we are talking about a non-magnum / short action rifle cartridge tested in a 16-inch barrel.
Of course, ultimately we are talking about Kinetic Energy and how can we relate these levels of energy to some other common object we are all familiar with. As perspective, the 300 yard energy of the 270 grain Speer BTSP. is equal to a 5 pound mass impacting at 108 miles per hour so think of your average household brick or a 5 pound sledgehammer impacting at over 100 miles per hour.
Velocity and Energy are only two indicators of performance, but are key contributors to on-target hunting performance which depends bullet expansion to create an optimum wound channel releasing the terminal energy to perform a humane harvest. In speaking with engineers at Nosler, Sierra and Speer, there is concurrence that rifle hunting bullets require a minimum on target velocity of 1800 fps to insure reliable expansion. Using an expansion factor of 1.5 times caliber, the .375 caliber achieves an expansion of .5625 inches which is exactly 9/16 inch for those that prefer fractional measurements.
When we compare the expansion of a .375 caliber bullet to what we have seen in actual hunting with the 45 RAPTOR (.625 inches for a 240 grain Hornady XTP MAG), the 375 RAPTOR achieves 90% of the expansion of the .452 bullet, but does so at a greater range, impacting with greater terminal energy, due to the improved ballistic coefficients of a rifle bullet over large caliber handgun bullets.
As a final thought on hunting performance, there has been a trend to larger and larger case capacity magnum cartridges to propel bullets at high velocity to extend that maximum point blank range further and further. Some of these new cartridges are so overbore that they forget the history of similar cartridges that became known for burning out barrels after 1,000 rounds or worse, burning out barrels at 500 rounds. In addition, what happens with many of these cartridges is that they over penetrate with the bullet exiting the game without transferring the kinetic energy to the game.
Historically, if we look at cartridges that have stood the test of time as great hunting cartridges, we see a common performance characteristic of the bullets fired from these cases impacting the game at a terminal velocity of between 1800 and 2400 fps which allows the bullet to reliably expand without over penetrating so that the full kinetic energy of the bullet is transferred to the game animal. While the idea of having a cartridge with a 500 or 600 yard maximum point blank range might sound exciting, the reality is that the majority of hunting occurs between 50 and 300 yards, not 400 or 600 yards. In fact, there are many very experienced hunters that consider 300 yards the maximum range they will ever take a shot for multiple reasons. These hunters see their ability to use concealment and stalking skills as essential to approaching game to a distance within 300 yards.
SHORT BARREL RIFLE PERFORMANCE
We have tested a 10.75-inch barrel using a carbine length gas system. Here are some initial results:
- 350-Grain Sierra Match King @ 1725 fps using AA 1680
- 175-Grain LeHigh Controlled Facture @ 2525 fps using AA 1680
We had a limited supply of LeHigh Bullets to do testing so we were only able to test the 175-grain with AA1680. We will be doing more supersonic testing with the 350-grain Sierra Match King and some other bullets we have been waiting on evaluating some additional powders with a similar burn rate to AA1680.
Subsonic use is best accomplished using Vihtavouri Tin-Star
VELOCITY VS. BARREL LENGTH
Having testing barrel lengths from 10.75″ to 22″, we have the following conclusions:
- When using faster burning powders, the velocity shift per inch of barrel length is approximately 15 fps as measured across barrel lengths from 10.75 to 18 inches.
- When using slower burning powders, the velocity shift per inch increases to as much 35 fps as measured using identical loads going from 10.75 to 18 inches. However, when you increase beyond 16 inches when testing identical loads, the barrel velocity change diminishes to approximately 15 fps per inch.
In conclusion, we find the ideal barrel length for most applications is between 18 and 22 inches. As an SBR, we selected a 10.75 inch barrel because that length fit within the profile of the DRD Tactical M762 rifle we use for SBR applications since it has a quick change barrel that allows changing to a longer barrel or other cartridges in about 2 minutes.
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