SOCOM Cancels Sniper System…Why?
…because a 300gr sniper bullet is a pipe dream…the desire for such a system belies a fundamental misunderstanding driven by the “bigs” trying to sell old technology with a new panache. The fundamental misunderstanding has two parts:
- Ballistic coefficient as a design focus in sniper systems is erroneous;
- There is a subtle untruth that by increasing mass, aerodynamic performance will automatically improve due to the higher ballistic coefficient.
An incorrect corollary to this misunderstanding is the idea that a 300gr bullet will also have better terminal performance due to greater kinetic energy. Let me explain.
First, the key property of a projectile is it aerodynamic stability. Aerodynamic stability depends on ratios, not just mass alone. This stability is rarely analyzed in bullet design because it’s difficult and costly. Lead-core bullets are made using older methods that typically cannot keep the tolerances to make aerodynamic ratios precisely, and that’s another reason for the lack of focus.
| Table 1: Changing Mass Only (this is not realistic, but what most people think will happen) | |||||||||||||||
| Mass (grains) | 220 | 230 | 240 | 250 | 260 | 270 | 280 | 290 | 300 | 310 | |||||
| Bullet drag coeff. | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | 0.3 | |||||
| G1 drag coeff. | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | 0.5191 | |||||
| I (form factor) | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | 0.5779 | |||||
| d (diameter) | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | 0.338 | |||||
| BC | 0.4760 | 0.4977 | 0.5193 | 0.5409 | 0.5626 | 0.5842 | 0.6058 | 0.6275 | 0.6491 | 0.6707 | |||||
Most people think like Table 1: ‘if I increase the mass, my BC will go up and I’ll have better performance.’ Table 1 also shows the common design approach focusing on a basic bullet shape, but adjusting the performance by increasing grain weight. According to table 1, the results should be pretty good as the BC, which is commonly used as a measure for performance, goes up significantly.
In table 2, we consider changing only the mass of the bullet with a muzzle velocity of 2700fps. In this case, realize that we don’t consider the aerodynamic properties which will degrade downrange velocity, so an aerodynamically superior design will have greater velocity on the target, and will more than offset the gains in mass.
Table 3 shows the results if we consider a change in velocity only. Notice how velocity changes make up for the mass increases in table 2. The additional benefit not shown in these tables is that the 236gr bullet will impact point on. Plus, the metal used by Dynamic Research will not “splatter” like a lead core bullet will.
| Table 2: Mass (at muzzle) | ||||
| Mass | 220 | 236 | 270 | 300 |
| Velocity | 2700 | 2700 | 2700 | 2700 |
| Kinetic Energy (Joules) | 4827 | 5179 | 5925 | 6583 |
| Table 3: Velocity (at muzzle) | ||||
| Mass | 236 | 236 | 236 | 236 |
| Velocity | 2700 | 2900 | 3100 | 3300 |
| Kinetic Energy (Joules) | 5179 | 5974 | 6827 | 7736 |
The problem with the approach in Table 1 is that it doesn’t work. What happens in reality when adjusting the mass of the bullet is that large trade-offs occur causes an increase in drag coefficient at a pace faster than the increase in mass. This lowers the overall performance of the bullet. Understand that the drag coefficient for a larger mass has to go up just because the additional mass must go somewhere. But, the other thing that happens is a reduction in the ratios of aerodynamic stability due to increasing mass without the ability to increase diameter. We’re stuck at .338, right? So, there is an optimum weight for a given caliber bullet that matches the aerodynamic features.
We’ve managed to discover a balance of mass and drag at about 236grains. With the aerodynamic properties at 236grains, if we can reduce the drag coefficient to, say 0.15, then this is pushing an equivalent BC of something greater than 1 as demonstrated in Table 4.
| Table 4: More Realistic (not real data, example only) | ||
| Mass | 236 | 300 |
| CD (drag coeff) | 0.15 | 0.4 |
| Cg1 (g1 drag coeff) | 0.5191 | 0.5191 |
| I (form factor) | 0.2890 | 0.7706 |
| d (diameter) | 0.338 | 0.338 |
| BC | 1.0213 | 0.4868 |
As you can tell, without changing the caliber, anytime you change the mass of the bullet, the drag properties will change significantly. This means that bullet mass should be optimized for a given caliber’s aerodynamic performance, not optimized for BC, which is actually the same as optimizing mass for the best mass. Doesn’t make sense, right?
Just ask a boxer and he will tell you speed kills. Kinetic energy is mass x velocity (squared) times one-half. So, increasing mass is actually less important than increasing velocity. Even kinetic energy penetrators focus less on mass, and more on speed. But they also focus on ensuring a point-first impact, which requires aerodynamic optimization, not mass or BC optimization.
The other thing that happens to a bullet in flight is that its velocity decreases much faster than its spin rate. This is important because it causes the bullet nose to point upward as it starts on the downward side of its trajectory. It means the bullet is flying like an airplane coming in for a landing, nose-up, instead of point-on trajectory. This makes things even worse because bullets don’t have wings to stabilize, so the oncoming air stream causes the bullet aerodynamics to change wildly and unpredictably.
The way to avoid nose-up bullet flight is through aerodynamic design, changing the form factor to maintain high velocities downrange. This does two things: 1. It keeps velocity high for greater kinetic energy; 2. It permits target interdiction point-on (many bullets will hit a target slightly or completely sideways at long distances).
Once again, kinetic energy should not be optimized using mass, it should be optimized using velocity which is performed by analysis of aerodynamic properties.
Going back to a 300gr design for a .338: it is not feasible to build a caliber-specific sniper system around a given mass. The sniper system must be built around aerodynamic properties of a projectile first. Then it must be implemented with appropriate metals to give the proper optimization of aerodynamic variables and weight. Finally, the rifle itself is built around the projectile. Oddly enough, the rifle, for most people, is the most expensive, most visible, and most desired item in a sniper system. In my opinion, it’s the least important.
If you want long-range precision and accuracy, build the right projectile first. Then fit the gun around the projectile.
Why did the PSR get cancelled? They figured 300grains was the optimizing variable to improve sniper performance in a .338 caliber weapon. I wish they would have asked Dynamic Research first, we’ve got what they need, but it’s not 300gr., it’s a 236 grain dose of reality that can repeatedly drill 10” groups at 2200m.
