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Originally Posted by CDAT
I am not sure where you are getting your information, but having shot level 3 plates with lots of different 5.56mm rounds if it is a level 3 plate it has to be rated to stop six separate rounds. So if a SAPI will not it is not a level 3 plate. The LE level 3 plates we shot would stop green (semi-AP) and even black tip (true AP) 5.56mm. At the shoots we did not get any vest to fail tell we were into the double digests of rounds. The manufactures provided the vests, we (the LE departments) the guns and ammo.
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I'm getting my info from the National Institute of Justice. The standards are that they test armor against 147grn 7.62mmN at @2780 fps ONLY. They do NOT test 5.56mmN in any of the NIJ Standards (I believe this is because LE wasn't using it when they wrote the initial testing standards in the 70's). The SAPI standard required stopping a 5.56mmN IN CONJUNCTION WITH an Interceptor soft plate (which is NIJ Level 3A) and NOT as a "stand alone" armor plate. this means you're backing an NIJ Level 3 plate with an NIJ Level 3A plate...in essence, giving that setup (in my game) an AV of 3. Most "stand alone" SAPI plates ROUTINELY perform at NIJ Level 3 (rifle) levels (which makes them no slouch in a "stand alone" configuration as well).
You may very well have had stops with 5.56mm, NO two manufacturer's armors are identical. Another factor may have been your rifles. If you were using actual M4's, their 14.5" barrels can reduce the velocity of the 5.56mmN by up to 300fps. The Level 3 plate does tend to stop any round NOT EXCEEDING 2750fps (and several rounds above 2800fps...cross-sectional density maybe?). Most testing in 5.56mmN is still done with a 20" barrel and the 3100fps velocity of M193 ball actually REQUIRES IT to hit 3100fps. Additionally, look at the new M855A1 ammo (with a 13% increase in velocity to more than 3100fps in a 62-grain projectile), It cuts right through an NIJ Level 3 vest at short range and STILL behaves like a Soft Point bullet inside the target. It could be as much of a "game changer" as MK282 was when it was introduced.
Check out both the Chopping Block and The Wound Channel on Youtube. They have the best videos of Level 3 plates being penetrated (usually by M193 ball due to its lighter grain weight/faster speed).
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As for the Level 4, the agency I was with had .30-06 custom Tungsten perpetrators designed to stop armored cars, the level 4 vests we shot that are only rated to stop one round, failed just after ten rounds in close to the same area (none of us were good enough shots to hit the same area, but we were all with in the X ring close to each other).
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I was wondering if you saw my mistake in the standards. I said one round when the standard is 3 rounds of AP. I'll make that correction today.
Once again, armor manufacturer's quality varies and there are several vests out there that EXCEED the minimum standard. I find it funny that the Standard is .30-06 AP, but that speaks to the age of the NIJ Standards as well (in addition to the state of "LE equipping" when they were written). Once again, 5.56mm (or 7.62mm) are NOT TESTED in this standard. The difference is that Level 4 plates ROUTINELY stop ALL 5.56mmN rounds...even though the velocity standard for this test is STILL only 2750fps (but with a hardened penetrator). ESAPI is, of course, a higher standard but any ESAPI plate is equal to, or better than NIJ Level 4.