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Question:

Why aren't bullets made of steel?

With the Reduced weight of steel,wouldn't the projectile be at a much higher velocity when fired causing more damage?I mean l couldn't steel be worked to seal the bore,not damage the rifling and still cheap enough to mass produce,and be light enough to carry much more ammo.

Answer:

Well trying to force that down a rifled barrel would be a funny trick. Please have a friend or two there to record it so they can put the blowing up of your rifle on youtube so people can learn what happens when idiots try stupid things. I'd say you should but you'll likely be dead or in hospital from the injuries. To expand your knowledge: Until you get to NIJ class 3 body armor any lead core high velocity bullet of FMJ form will go through like it's not even there. Oh pretty much anything with soft point ammunition at over 2,000fps velocity will go through with devastating effect. So lets see .. oh yes time to ban the .30-30 Winchester for civilian use. All the typical rifle caliber ammunition designated by the military as armor piercing has a copper alloy jacket around either a hardened steel core or more commonly a lead core with a hardened steel or tungsten alloy penetrator centered in that.
Okay one side note before going into the main issue. Steel is really really hard on rifle barrels. Okay, so the most common lead 9mm bullet weighs 124 grains. If all that was wanted was higher velocity, you could switch to a 115 grain bullet (which some people do), or even a 90 grain bullet if you are a reloader. (You see 90 grain bullets for 380 acp ammo, that same bullet could be reloaded onto a 9mm cartridge) But velocity alone doesn't give power. That's why a 115 grain 9mm bullet going at it's standard velocity does less damage than a 45 acp's 230 grain bullet going at it's standard velocity, because it weights twice as much and yet is going only a little bit slower But now go out to your front yard and grab a ping-pong ball and a rock about the same size. Throw them both as hard as you can. The ping-pong ball while lighter didn't go very far did it. See, the ratio of surface area to overall weight of ping-pong ball is very high, so air resistance works on it a LOT. And that is what makes lead so great for projectiles. It is dense so you have a very small surface area per unit of weight meaning that a steel bullet may beat lead in initial velocity but just 50 feet out the lead bullet would be going pretty much the same speed and at 100 yards out the steel would be dramatically slower. Note this is the same reason why 'secret sniper ice bullets' would never work even if you could get it to not melt...it's just too light. Ever hear of tanks and airplanes firing DU ammo? That stands for Depleted Uranium, it is something that is even more dense than lead which is why it makes an even better bullet than lead
The bullet needs to be a bit malleable to conform to the grooves in the barrel. In an American .30 gun a .308 bullet is forced out of the gun it has to conform to the .30 bore and .308 grooves to form a tight seal. That's why lead and copper are the primary materials of the bullet. A steel bullet in a steel bore would potentially produce a pipe bomb or at least do significant damage to the bore. Also, the weight of bullets are optimized for their application with the current materials. There is no need or desire to reduce the mass of the bullet. Simply reducing mass for increased velocity can effect the terminal ballistics in all kinds of ways, but you cannot assume that damage will be higher for a variety of reasons. If nothing else the fact that the military has INCREASED the 5.56x45mm from 55gr to 62gr should be enough to doubt your claim. Also steel is about 70% the density of lead, so there would not be a major savings in mass, but aluminum is only 25% the density and it is much closer to the hardness of lead. If you really wanted a light bullet, the aluminum may be the way to go.
As others have mentioned, steel lacks the ductility to conform to rifling and seal the bore. Cannon projectiles, which usually are made of steel, overcome this problem by using one or more driving bands of softer metal, usually brass or bronze, but sometimes even plastic, on the circumference of the projectile, usually close to the base. The body of the projectile rides on the lands, while the driving band fills the grooves, seals the bore and imparts the stabilizing spin to the projectile.

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