Better than M4, but you can’t have it

[Dominique R. Poirier]

The reason for using lead to manufacture bullets owes to two or three main reasons which constitute an advantage over nearly all other metals:

is at the same time heavy and soft;
it is inexpensive.

I explain why. Lead is a metal soft enough to be easily shaped in a rifled barrel without generating significant and dangerous increase of pressure during the combustion of the powder. A classic rifle’s barrel firing fast and powerful ammunition can undergo pressures as high as 3,500 to 3,800 metric kilo per square centimeter (or bar). For the purpose of comparison, the maximum pressure allowed in a 12 gauge shotgun barrel is about 1,200 bar.

Other metals such as steel or tungsten carbide, for example, are unsuitable for rifled barrels because they are too hard metals to take the shape of a rifled barrel. They would just make the barrel blow up if ever someone attempted to use such a bullet in a rifle. That’s why there is a need to jacket or to circle these metals into or with softer metals such as copper.
In the case of big calibers relevant to the field of artillery (say, above .50) the recourse to copper-circled shell entails a relatively fast wear of the barrel because the shell is in steel and not copper-jacketed (there are many interesting things to say about this point and I’ll be pleased to elaborate on this other fascinating subject if ever someone is interested in artillery from 30mm caliber on).

Actually, the best metal for a rifle bullet should be platinum because it is heavy, harder than lead, and it can bear much higher temperatures than lead. But platinum is too rare and too expensive to be shot.

We are constantly looking for heavy metals to manufacture bullets because there is a need to keep the maximum kinetic energy possible as long as possible. Air density tends to slow a bullet speed; therefore the best remedy to that problem is to make a bullet as heavy as possible for a given diameter. Also, more kinetic energy means better perforating power, of course (let me brush aside the question of stopping power for a while, which would make me wandering from the matter at hand).

Impoverished (or depleted) uranium is still a better metal that lead, owing to its weight; but there are many problems with that metal. Impoverished uranium is uranium remaining after removal of the isotope uranium-235. It is primarily composed of the isotope uranium-238. Since depleted uranium contains less than one third as much uranium-235 as natural uranium, it is weakly radioactive and an external radiation dose from depleted uranium is about 60% of that from the same mass of uranium with a natural isotopic ratio. At standard temperature and pressure it is a very dense metal. Due to its high density the main uses of depleted uranium include counterweights in aircraft, radiation shields in medical radiation therapy machines and containers for the transport of radioactive materials. The military uses depleted uranium for defensive armor plate and its pyrophoricity has made it a valued component in other military applications, particularly in the form of armor-piercing projectiles (anti-tank 30mm shells for General Electric machine guns on Fairchild A-10 airplanes, as best example).
Try to saw a bar of impoverished uranium with a mere metal handsaw and you’ll see an amazing shower of sparks as if you were doing the same with a powerful metal electric saw against ordinary steel… Metal temperature rises considerably during this simple experiment owing to friction and to the atomic weight of this metal.
Depleted uranium behaves in the body as natural uranium does and that’s why it would be unethical to currently use it against humans in small arms.

Now, the problem we have with lead is its very low melting point which is 621.43 °F only. Using full lead bullets in firearms is possible as long as the speed is not in excess of about 1,300 to 1,500 feet per second. These melting point and hardness can be slightly modified by the adding of antimony in it. Beyond 1,500 feet per second a lead bullet melts, buckles, and no longer takes the shape of a rifled barrel. As a result it totally loses in accuracy; even at short distances. That’s why we jacket it with copper, another relatively soft metal whose melting point is much higher.

About “boat tail” shaped bullets.

This shape has been invented first circa 1900 by the French Army, though I am not sure if they were the first to discover it (other and discrepant clues are welcome). Anyways long range rifle shooting competitions commonly existed in France during those earlier times. Shooting distances were of 1,000 meters. Targets were horsemen silhouettes and the rifles and ammunition shooters used was the Lebel rifle model 1886 M-93 in 8mm Lebel. Full metal jacket boat shaped 8mm bullets just did it the best.
Actually, the boat-tail shape has been the best aerodynamic shape offering the best accuracy to a bullet or a shell until then, and that why it is largely used nowadays in small military arms and in artillery as well.

“Personall I hunt with a 257 weatherby mag. IT is 25 caliber bullet on a 7 mag casing. It moves with a 100 Seirra Boat tail at about 3700 FPS.”

Yes, your choice of Sierra bullets is a good pick and the best I know and experimented with that caliber is the Sierra Match 100 which is a FMJ boat-tail shaped bullet (the same as yours, it seems). You may improve the kinetic energy and the stopping power in using round nose shaped bullets, but this will be done at the expense of accuracy at long distances when compared with the former.

Weatherby ammunitions are characterized by their higher speed and power and are very good ammunitions for hunting. Weatherby hunting rifles are heavier and more expensive than other standard rifles because the particular ammunitions they use develop unusually high pressures. This explains why the case of any Weatherby cartridge is reinforced at the bottom. If not, the cases would often break up under pressure.

Now, bear in mind that speed is not synonym of accuracy; quite on the contrary. I will explain why with more details in another comment, if ever you want it, since it would make this one much longer.

“The 308 dose not really have that great of ballistics, their are much better rounds when it comes to that.”

Sorry to disagree a bit, but the .308 is the best compromise one can find nowadays when considering modern military ammunitions for small arms. A similar equivalent in the civilian realm is the .300 Savage which offer a very good accuracy.