I usually do not like to get into these threads about designing the ideal military service round or the next gen assault rifle, but I've had an idea for a while that I think holds some water.
The never-ending debate about the ideal military cartridge typically revolves around factors that can be attributed to three main characteristics of the round: caliber, weight, and velocity. These three characteristics are related in many ways, and together make up for the explanation of other important considerations such as recoil, trajectory, and terminal effectiveness.
Before I get into what I'm thinking, I'd like to cover some of the relationships between these elements.
For a given caliber, if you increase caliber without increasing weight, velocity will increase (the .30-06 family is a good example, notice how the top loads in .35 Whelen produces .300-Win-Mag-like velocities for equal weights)
The increase of caliber without increasing weight also hurts the BC-potential of bullet. While weight and caliber do not explicitly determine the BC, they do create limitations on it. To go along with the .300 Win Mag-.35 Whelen comparison, just compare the BC of a 220 grain .308 bullet to a 220 grain .358 bullet. One is match-grade, one is ho-hum.
If you combine the two above listed relationships, increasing the diameter without increasing the weight of the bullet gets you a round that will punch a larger hole and shoot faster initially, but it will also suffer more wind-drift, bleed velocity faster at distance, and have less sectional density for deep penetration.
So given some of these trade offs that limit conventional bullet design, what if you could get around them by changing materials? My thinking is to possibly go with a copper-jacketed, aluminum core bullet. Because aluminum is so much lighter than lead, you could easily increase caliber without significantly adding weight and without seriously compromising aerodynamic qualities. I'm thinking aluminum primarily because it is almost as cheap as lead and not so hard that it would damage the rifling.
Aluminum is roughly 1/4 the density of lead, so for the sake of simplified modeling and assuming the weight of the jacket is negligible compared to the typical lead core, you could have a bullet with roughly 4 times the volume and similar weight. If you modeled a bullet as a simple cylinder rather than a streamlined bullet, this means you could either A) keep bullet diameter constant and increase bullet length by 4 times [serious tumbling damage, also super fast twist rate required], B) maintain bullet length and double bullet caliber [for a .223, you'd wind up with something roughly shaped like a .45 hardball, not the best for distance], or C) anything in between such as proportional increase of length and caliber [I'd think this would be best].
So the advantages would be:
-improvement in aerodynamics/drag coefficient for a given caliber/weight ratio
-increased caliber/bullet length without adding weight (bigger hole in bad guy)
-related to above, increasing caliber without adding weight can increase muzzle velocity for a given parent cartridge (pressure x area = force)
-many of the benefits of a full-power rifle cartridge with intermediate-rifle recoil
Disadvantages would be:
-decrease in sectional density (bullets wouldn't have as much driving momentum to burrow through soft targets). The best way to mitigate this would be to make more use of increased bullet length rather than increased bullet caliber
-drag coefficients are only part of the equation, increased volume without increased weight would still be somewhat more susceptible to wind-drift and velocity loss than an identically-shaped, equal-weight bullet.
-increased velocity from increased caliber may be negated by increased bullet protrusion into case and bearing surface (for reloaders out there, think Barnes solid copper bullets)
Anyway, what do you guys think? I know it isn't truly revolutionary or anything, but it seems like a set of often-overlooked observations. Aluminum was just my initial idea. It may actually have too low of a density value, but it is cheap and plentiful. Steel cores (nothing new) have some of the similar advantages above but in a subtler form (the difference in density between lead and steel isn't as drastic). A use of a composite copper-aluminum-lead bullet could provide many of the advantages listed above and induce some crazy terminal effects seen in the 5.45x39 5N7.
The never-ending debate about the ideal military cartridge typically revolves around factors that can be attributed to three main characteristics of the round: caliber, weight, and velocity. These three characteristics are related in many ways, and together make up for the explanation of other important considerations such as recoil, trajectory, and terminal effectiveness.
Before I get into what I'm thinking, I'd like to cover some of the relationships between these elements.
For a given caliber, if you increase caliber without increasing weight, velocity will increase (the .30-06 family is a good example, notice how the top loads in .35 Whelen produces .300-Win-Mag-like velocities for equal weights)
The increase of caliber without increasing weight also hurts the BC-potential of bullet. While weight and caliber do not explicitly determine the BC, they do create limitations on it. To go along with the .300 Win Mag-.35 Whelen comparison, just compare the BC of a 220 grain .308 bullet to a 220 grain .358 bullet. One is match-grade, one is ho-hum.
If you combine the two above listed relationships, increasing the diameter without increasing the weight of the bullet gets you a round that will punch a larger hole and shoot faster initially, but it will also suffer more wind-drift, bleed velocity faster at distance, and have less sectional density for deep penetration.
So given some of these trade offs that limit conventional bullet design, what if you could get around them by changing materials? My thinking is to possibly go with a copper-jacketed, aluminum core bullet. Because aluminum is so much lighter than lead, you could easily increase caliber without significantly adding weight and without seriously compromising aerodynamic qualities. I'm thinking aluminum primarily because it is almost as cheap as lead and not so hard that it would damage the rifling.
Aluminum is roughly 1/4 the density of lead, so for the sake of simplified modeling and assuming the weight of the jacket is negligible compared to the typical lead core, you could have a bullet with roughly 4 times the volume and similar weight. If you modeled a bullet as a simple cylinder rather than a streamlined bullet, this means you could either A) keep bullet diameter constant and increase bullet length by 4 times [serious tumbling damage, also super fast twist rate required], B) maintain bullet length and double bullet caliber [for a .223, you'd wind up with something roughly shaped like a .45 hardball, not the best for distance], or C) anything in between such as proportional increase of length and caliber [I'd think this would be best].
So the advantages would be:
-improvement in aerodynamics/drag coefficient for a given caliber/weight ratio
-increased caliber/bullet length without adding weight (bigger hole in bad guy)
-related to above, increasing caliber without adding weight can increase muzzle velocity for a given parent cartridge (pressure x area = force)
-many of the benefits of a full-power rifle cartridge with intermediate-rifle recoil
Disadvantages would be:
-decrease in sectional density (bullets wouldn't have as much driving momentum to burrow through soft targets). The best way to mitigate this would be to make more use of increased bullet length rather than increased bullet caliber
-drag coefficients are only part of the equation, increased volume without increased weight would still be somewhat more susceptible to wind-drift and velocity loss than an identically-shaped, equal-weight bullet.
-increased velocity from increased caliber may be negated by increased bullet protrusion into case and bearing surface (for reloaders out there, think Barnes solid copper bullets)
Anyway, what do you guys think? I know it isn't truly revolutionary or anything, but it seems like a set of often-overlooked observations. Aluminum was just my initial idea. It may actually have too low of a density value, but it is cheap and plentiful. Steel cores (nothing new) have some of the similar advantages above but in a subtler form (the difference in density between lead and steel isn't as drastic). A use of a composite copper-aluminum-lead bullet could provide many of the advantages listed above and induce some crazy terminal effects seen in the 5.45x39 5N7.
