MEPLATS AND IMPACT EFFECT
The meplat is the frontal circular flat of a flatnose bullet that first comes into contact with game. The size or diameter of the meplat effects the performance of a cast bullet in a number of important ways. Among these are terminal stability, bullet length and subsequent power generation efficiency, wound channel diameter, rate of incapacitation, aerodynamics, and, in lever-action rifles, magazine safety. We take the view, common to experienced users of large caliber cast bullets, that a large frontal flat or meplat is essential in producing quick and humane kills on big game.
Terminal Stability
Terminal stability refers to a bullet's impact characteristics. Upon impact, a bullet can be expected to penetrate the game animal. However, a bullet's path through game tissue, whether it is straight, deep, or angular, is largely determined by its construction and design characteristics. Primary among those characteristics is the weight carrying capacity of the front of the bullet. Bullets with less weight in the forward half of the bullet, as compared to the rear half, tend to be less terminally stable and tend to exhibit characteristics such as yaw which reduce penetration depth, than bullets that carry similar amounts of weight in the front and rear. Since bullets with wider or broader meplats tend to carry more weight up front than bullets with smaller meplats, they tend to be more terminally stable and, as a consequence, produce deeper and straighter penetration channels. This is most apparent with relatively short bullets such as those used in handguns. The mechanics associated with this are pretty clear. When a bullet carries significantly more weight in the rear than in the front, there is a definite tendency for the rear of the bullet to overtake the front of the bullet upon impact. In other words, the bullet tends to go sideways. This is due to the complete loss of aerodynamic stability that occurs upon impact, and the greater momentum of the rear of the bullet when compared to the lighter front end of a small meplated bullet. This is especially important for those shooting the handgun, since smaller meplats have a relatively greater effect on the front to rear weight-carrying ratio of the bullet, since the bullets are shorter. When the subject turns to rifle bullets, especially the longer bullets that characterize heavy 45-70 bullets, the influence of meplat diameter on the front to rear weight ratios is generally less relevant to terminal stability, since the bullets are longer. Meplat diameter does, however, contribute to bullet length, with wider meplated bullets exhibiting shorter overall length than smaller meplated bullets of the same weight. This is quite relevant to the 45-70, as overall cartridge length is a critical measurement that cannot be exceeded if the cartridge is to chamber properly. Consequently, given a cartridge of a specific length, the cartridge with the shorter bullet possesses less seating depth, and as a result provides more room in the cartridge case for gunpowder. Simply stated, such a bullet can produce more power at the same pressure, or equal power at lower pressure, when compared to a bullet with greater length. Since broader meplated 45-70 bullets tend to be shorter at any given weight, they tend to provide a superior power to pressure ratio.
Wound Channel Diameter
The diameter of the wound channel produced by a proper hard-cast bullet is far more a product of the diameter of the meplat than the diameter of the bullet. This is of critical importance. As a consequence of this, wound channel diameter and the resulting speed of incapacitation can be substantially increased through the use of hard-cast bullets with broad meplats. This is readily observable through wet newspaper penetration testing, or by the careful postmortem examination of big game animals. Interestingly, as can be verified by testing, relatively small increases in meplat diameter produce relatively large increases in wound channel diameter. This is great news, as increased meplat diameter not only contributes to improved terminal stability and power to pressure ratios, it also produces substantially larger wound channels and faster incapacitation. We have observed this in our 44 Magnum and 45-70 
production. Interestingly, our 540-grain Hammerhead for the 45-70 produces penetration channels or wound channels that appear to be fully twice the diameter of our 420-grain Hammerhead for the 45-70, yet the difference between the bullets' meplat diameters is only .030-inch. Our 420-grainer sports a meplat diameter of .330-inch and our 540-grainer sports a meplat diameter of .360-inch. What is also clear is that our 420-grainer with its .330-inch meplat produces wound channels substantially larger than those produced by the .300-inch meplat that is all to common to the caliber, and characterized our early efforts in 45-70.
Further considerations
Although broader mepated cast bullets generally produce larger diameter wound channels, sometimes, especially at the relatively high velocities produced by medium weight 45-70 bullets, impact stresses can be great enough to deform the meplat and effect the size and characteristics of the wound channel. Occasionally, when impact occurs at short range into heavy game even the toughest hard-cast bullet will deform at the meplat, reducing its diameter. This is most often observed when the impact occurs at short range into heavy bone, when impact velocity is relatively high. This is one of the primary reasons we offer our very heavy 540-grain Hammerhead, as its extra weight mandates a lower velocity, which tends to protect against significant meplat deformation when engaging the heaviest game. Since game such as buffalo and elephant are invariably shot at short range, logic strongly argues for a heavier bullet at lower velocity. In this way, the major determiners of impact stress, the speed of impact and the toughness of the target, do not tend to overwhelm the strength of the bullet. However, in the great majority of shooting circumstances broad meplated hard-cast bullets, such as our 420-grain Hammerhead, can be depended upon to produce substantially larger wound channels than smaller meplated hard-cast bullets and also provide faster incapacitation. Whereas smaller meplated bullets appear to never produce the large diameter wound channels normally produced by broader meplated bullets, unless they are sufficiently soft to cause expansion, which always limits penetration. This is the primary reason why we have designed our SuperHardCast Hammerheads with the broadest meplats available.
- Randy Garrett