Different formulas for bullet jackets have come and gone, the industry standard is "gilding metal" which is 95% copper, 5% zinc, which makes it actually a brass alloy. Different allows, cupronickel, tin, even steel have all been tried with various levels of success.
|7x57 loads by Kynoch, far left representative of the original 173gr load|
Note this number, 2,400 fps, it comes up a lot. The 416 Rigby, a "Safari" stopping cartridge used a 400 grain bullet at 2,400 fps. The 375 Holland and Holland used a 300gr bullet at 2,400 fps.
So, you are asking, since we have smokeless powder, modern primers, brass, and firearms, why the sedate velocity? That is a very good question. The first answer is that not all smokeless powder is created equal. The British Cordite propellant and other nations smokeless propellents were not mixed with burn controllers or coated with burn regulators. So in terms of ballistics, you "got what you got" from a propellant and had to make the most of it. And if you have to make the most of it, go for Accuracy and Penetration. So the heavy for caliber bullets at moderate velocities continued to dominate. Even the 30-30 Winchester is famous for using heavy bullets for the powder charge given.
|6.5 Carcano wound profile, similar FMJ RN wound profile for 7x57 173gr FMJ RN loading or 6.5 Mannlicher, or original 6.5x55 military load. Note the deep, straight penetration.|
FMJ bullets are a "cup and core" bullet. The jacket is drawn first, then the core is inserted, lastly the jacket is rolled over the base of the core to keep it locked in place. This rolling over the base of the bullet is why FMJBT bullets are not used for competition by serious competitors. The Open Tip Match (OTM) or Hollow Point Boat Tail (HPBT) is a reverse drawn jacket, meaning that the core is put in from the front, and then the jacket is smoothed down to form the nose ogive. This puts the "folding" errors of the final step much closer to the center of rotation (increasing stability) and gives the match bullets a much more uniform base.
Traditional soft nose hunting bullets, flat base or boat tail, are built the same way as the competition bullets, save that the lead is exposed in order to provide expansion. Various methods of keeping the jacket together with the core to provide stability to the core have been done over the years, from metalic bonding to locking rings. Some premium bullets abandon the tradition drawn jacket and core method, such as the Partition, which puts a solid gilding metal divider between the front core and the back core.
|6.5mm Berger 140gr hunting VLD. Total separation on a deer shot from a 6.5x284 Photo by BigShooter of californiapredatorsclub.com|
|Courtesy Dr. Martin Fackler|
Now you can put it all together as to why Bell was shooting elephants with a sedate 7x57. The FMJ load was heavy, giving good sectional density and very little deformation to ensure excellent penetration, and the velocity was adequate to get the bullet where it needed to be. On a different note, after switching to a heavier rifle, Bell commented that some of his "inexplicable misses" suddenly went away.
However, let us go away from the first quarter of the 20th century. Roy Weatherby has succeeded in igniting velocity fever, and normal bullets aren't getting more lethal, in fact they are going so fast that when they hit they open up completely before penetrating deeply. This causes a lot of wounds, but poor immediate lethality.
There are two answers to this. The first answer is: Use heavier bullets at a reduce velocity. Shooting a 150gr bullet at 3,400 fps into ballistics gel will show you that it won't penetrate nearly as well as a 220gr bullet at 2,800 fps. Mass gives momentum, and momentum allows for penetration.
So there you have it, smokeless powder combined with better bullets gave rise to the velocity craze. It should be noted that powder improvements have allowed even sedate old standby rounds to get a new lease on ballistic life. The 375 Holland and Holland can be loaded a bit faster than 2,400 fps with a 300 gr bullet now that it is not dependent on cordite.
I have not gotten into monolithic bullets here, or bullets where the gilding metal is used as the expansion portion of the bullet. Nor have I covered other metals added to bullets to increase armor piercing attributes. That however, will be another post.
On the pistol front, there was no velocity revolution to cause any sort of new designs to come out requiring metal jackets. Metal jacketed pistol bullets are generally around simply to allow shooters to not have to deal with barrel leading, and Hague treaty compliance for military forces (in FMJ form). All other traditional jacketed type of bullets are simply gilding metal clad variations of their pure lead counterpart. More exotic types of handgun projectiles will be covered later.