We recently came across this video on YouTube. It is certainly one of the more interesting and better produced of the videos about Polycarbonate and bullet resistance.
We will concentrate our discussion to the first two rounds fired, the 0.22LR and the 9mm round.
Most ballistics certifications for bullet resistant glass constructions, such as UL.752, start their testing with a 9mm Full Metal copper Jacket with a lead core. This bullet weighs 8 grams and has a test velocity of 358 m/s. The 0.22LR in the video has a weight of about a third of this at 2.6 grams and a velocity of around 290 ms.
Using our Kinetic Energy formula of Energy = 0.5 x Mass x Velocity x Velocity, the 9mm round has about 4.7 times the energy of the 0.22LR round.
For the UL.752 Level 1 test three shots of a 9mm FMJ must be fired at a 12" x 12" target and the shots must land within a 4" triangle area. To pass the test no bullets must pass through the material and no pieces of the material must come off the back with sufficient velocity to damage a cardboard witness plate located a short distance behind the sample.
The 12" x 12" test piece is fully supported and will not move during the testing.
From the video of the 022LR it is clear that the 0.5" Polycarbonate does not allow the round to pass through. One concern that we would have is that the test piece was not supported, so some of the energy was absorbed by moving the piece when it was hit. That would not be realistic in real life where a window would be supported. Also the test in video did not consider multiple hits in a small area as in the UL.752 Level 1 test. However, it appears likely that Polycarbonate that is supported in a frame could stop 0.22LR rounds at a reasonable thickness - however, without testing in a controlled manner it is not possible to say whether the required thickness is 0.5" or greater.
From the video of the 9mm round, two 0.5" pieces of Polycarbonate were clamped together. This test was designed to see if 1.0" of Lexan could stop a 9mm round. We have some similar concerns as for the first test where the test sample was not supported. More importantly the pieces broke free from the clamp and it is not clear whether the second piece was hit straight on or whether the bullet glanced off the piece. We don't think that the video is claiming that a 1.0" piece of Lexan can stop one or more hits from a 9mm round but we would be concerned if someone inferred this from the video.
One thing that we do know is the a 0.75" construction made from 1/8" Polycarbonate - 1/2" Cell cast Acrylic - 1/8" Polycarbonate can be tested to UL.752 Level 1 with the 9mm threat and will pass. So a single 1,0" supported layer of Polycarbonate may or may not be effective for stopping 9mm rounds but there are potentially cheaper and lighter options available that will.
If you put thick enough piece of Polycarbonate in front of a 9mm round it will eventually stop the round. It just may not be the cheapest or lightest way of doing it, which is why Polycarbonate is not normally tested and approved as a bullet resistant material as a stand alone solution.
The video even states that their test is completely unscientific.
All of this does not make the video any less interesting or enjoyable. It is also very well produced.
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Yup, a fun video. Regardless of the unscientific nature of it, it does show that PC is pretty tough stuff.
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Please let us know what the "cheaper and lighter" alternative to 1" polycarbonate would be.
ReplyDeletethe ebay prices for 1/2" polycarbonate are about 25% the price of Makrolon Hygard BR750. if you can get me BR750 level protection yet cheaper than two plys of 1/2" polycarbonate, you have a deal.
You are correct, the price of two pieces of 0.5" Polycarbonate is about 25-30% of the price of a similar sized piece of BR750 (which is a 0.5" piece of cell cast acrylic with a piece of 1/8" Polycarbonate on each side).
DeleteThe reason for the increased price is that to make the laminate you need to add a material to bond the Polycarbonate to the Acrylic and then heat the laminate under a high pressure in an autoclave to bond the pieces together. All of this process is expensive.
If you take the two 0.5" pieces of Polycarbonate you would still need to bond them together or hold them together in some sort of frame, both of which can be expensive processes. The overall cost of using two pieces of 0.5" Polycarbonate would be similar or more expensive than the BR750 once these additional costs are considered and it would certainly be heavier. Also, you would need to verify by ballistics testing that the 1.0" of Polycarbonate can actually stop the same threat level as the BR.750; the acrylic's purpose in the BR.750 is actually to shatter and absorb the energy of the bullet. An all Polycarbonate structure does not behave in the same way and although it is thicker, may not have the same bullet resistance.
Even though the BR.750 meets UL.752 Level 1 bullet resistance, it is probably not the thinest and lightest solution to meeting the Level 1 requirements. The Polycarbonate on the front face does very little (other than ensure that if the material is installed the wrong way around it will still work). The Acrylic absorbs the energy and the back piece of Polycarbonate stops and fragments breaking off the laminate after it is hit by the bullet. It is certainly possible that a laminate consisting of a 0.5" piece of cell cast (not extruded) acrylic with a piece of 1/8" Polycarbonate on the back face could meet UL.752 Level 1 requirements, but this would need to be confirmed by ballistics testing. The material would also have to be installed the right way around.
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