Ar500 steel plate can stop rifle bullets. In my brain I’m thinking like “well if kevlar is stronger than steel, then slab of kevlar of the same size of an ar500 plate should stop rifle bullets too”. Clearly it doesn’t and I don’t understand why
In: Engineering
Kevlar can absolutely stop rifle bullets, with enough layers. Enough layers of anything can stop rifle rounds. The issue is weight and mass. A Kevlar vest that would reliably stop a, let’s say, 30.06 ball round, and not leave you with kinetic damage from the impact as discussed in other comments (broken bones, ruptured organs, internal bleeding, etc) would be ridiculously thick. One would looked like Michelin Man, or Stay Puft. Steel or ceramic is added to the armor as plates to cut down on the thickness required. So.e of the first bulletproof armors were just layered silk shirts, but to be fair that was back when black powder and round shot was king of the day.
Paul Harrell in his videos demonstrates repeatedly when shooting either the meat target or Shasta bottles that several layers of fleece will stop rifle rounds (after going through meat and oranges or 2liter soda bottles).
it’s not just about strength. PSI is a factor.
basically the way kevlar works is it deforms around the bullet to catch it while dissipating a lot of the kinetic energy but also stopping the bullet from putting a hole in your body (that’s why even if you take a shot with kevlar on you should still probably see a doctor). if it was just a steel plate then (in addition to it being heavy) with 0 deformation the kinetic energy of the bullet (assuming it didn’t penetrate the plate) would be entirely dispersed into your body.
pistol bullets have a lower muzzle velocity but also tend to A not be jacketed, B are more likely to be hollow-point (hollow point being illegal in warfare but actually preferable in a lot of pistol situations) and in general have a lower PSI on impact than a rifle round typically
so kevlar saves you because it’s tough but ironically kind of soft but the issue with a rifle round is that because it’s very fast and very had and very pointy is it’ll cut the kevlar like a knife. so what the metal plate does is basically turn the rifle round into something less pointy and less directed so it won’t penetrate the kevlar.
mythbusters did a thing that uses similar principals but on a different scale where they were testing (from burn notice) whether or not you can use a phone book to make a car bulletproof. so first they just shot a car door and the bullet went through no problem. then they shot a phone book and the bullet made it all the way through. but then they put the metal of the door in front of the phone book the metal broke up the bullet enough that the bullet then couldn’t make it all the way through the phone book
Thin, pointy, and fast pokes a better hole than thick, blunt, and slow.
Try poking your finger through a sheet of paper and then try a pencil.
Most rifle projectiles are pointier and smaller in diameter.
Now add the velocity to the equation.
Rifles tend to utilize more powder due to a larger casing. More powder, more fast (there are also different powder burn rates at play here)
Their casing is bottle necked, increasing the pressure. Gases escaping smaller hole means higher pressure.
The projectile is sometime lighter than that of a pistol projectile. Lighter objects are easier to move.
This is how you can get rifle rounds that will move 3X the velocity of a pistol round.
Even steel struggles with rifle rounds sometimes. Rifle rounds generally travel much faster than pistol rounds and are smaller in diameter. The combination of speed and small area create a tremendous amount of energy concentrated in a very small area. Pistol bullets get caught by the layers of Kevlar like a tightly woven net, rifle bullets tend to divide some fibers of Kevlar and tear the ones that they can’t divide.
Pica of what a rifle round can do to AR500. This was a 22-250 that was firing at around 4350fps. Target was 60ish yards out.
The energy at the moment (physical) of impact is greater than the tensile strength of the weave. So it rearranges the structure of the kevlar mat creating a hole.
Steel is one single solid structure.
Kevlar is a bunch of special interwoven fibers. Even though they’re strong, there are still ‘holes’ in between them. If something goes fast enough, it can just push the fibers aside and go through the holes.
The steel has no holes, so the rifle bullets just squish it down instead.
Stopping pistol rounds and rifle rounds are very different things. Rifle rounds are moving much, much faster and are generally smaller in diameter. Kevlar vests are made of layers of woven fibers and work by catching the bullet and slowing it while preventing it from piercing the wearer. Hard body armor,steel and ceramic, both rely on being made of harder materials than the projectile and shattering the incoming round, with ceramic composite and similar armor they also catch the fragments, with AR500 it does not, and the bullet fragments fly off roughly parallel to the plate surface, this is what is typically called “spall”
Also AR500 is bad armor, doesn’t have NIJ ratings, is really heavy and can be generally defeated by 5.56 M193 ball out of a 20″ barrel within 100 yards.
There are 2 ways to stop a bullet: you can catch it, or break it up.
To catch it you use a high tensile strength fabric or other material to catch it like a net. Howver, faster pointier bullets just split through the fibers like a needle.
For fast projectiles you need a hard material to damage the projectile’s tip enough for the fibers to catch it. Steel and ceramic are very good at damaging projectiles, and ceramic is good at absorbing energy by fracturing.
Ultra-high velocity projectiles need to be stopped with spaced armor, such as what’s used on the ISS to protect against meteorites.
The problem is it’s stronger on a weight basis, not necessarily a volume basis. The reason Kevlar works as body armor is because you can have a vest that’s not excessively heavy with the ability to stop certain rounds. It also acts in a way that disperses the impact across your torso. So it’s possible to make a Kevlar vest that can stop a high-energy rifle bullet. The problem is the vest would be too big and too heavy.
It’s mostly a combination of speed and bullet design. Faster bullets tend to have a lot more energy because energy is proportional to the velocity squared. Rifle bullets can go 2-3x faster than a handgun, which means 4-10x the amount of energy.
With bullet design, rifle bullets tend to be pointy and long, this is called a spitzer bullet, handgun bullets are more blunt and short and fat. With a long pointy bullet, when it hits the kevlar they put their energy into a smaller area on less fibers, making it more likely the kevlar will fail. You can see it action if you look up 300 blackout, it shoots a spitzer bullet at the same speeds as a handgun, and it can penetrate kevlar vests just because of the long pointy bullet.
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