Wikipedia -- Personnel Armor System for Ground Troops wrote:The Personnel Armor System Ground Troops Helmet, also known as the "K-pot" and also the "Fritz" helmet for its resemblance to the World War II German army helmet is a standard infantry combat wear in the US Military. The shell is made from 19 layers of Kevlar, a ballistic aramid fabric treated with a phenolic resin system and is rated at a Threat Level II, and offers protection against fragmentation and ballistic threats. It meets the 1800 requirement of MIL-STD-662 E. It weighs from 3.1 pounds (size extra small) to 4.2 pounds (extra large).
The PASGT Helmet is said to have stopped rifle rounds on occasion, most commonly 7.62x39mm (AK) rounds (in one account the PASGT Helmet is credited with stopping an M43 round from approximately 25 meters). This performance would be closer to Level III or Level IV performance, though in a demonstration of the Heckler & Koch MP7 on the Discovery Channel show Future Weapons, a PASGT helmet suffered a catastrophic armor penetration when hit head-on with one round of the MP7's 4.6x30mm ammunition. Similarly, the firearms testing site The Box o' Truth has reported that a 7.62x25mm Tokarev fired from a ČZ vz. 52 handgun was able to penetrate the helmet at 25 meters. In the same test, both the 5.56x45mm NATO and the 7.62x39mm were able to yield catastrophic penetrations through both sides of the helmet.
Wikipedia -- Threat Level II Ballistic Vest wrote:This armor protects against 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets, with nominal masses of 8.0 g (124 gr) at a reference velocity of 367 m/s (1205 ft/s ± 30 ft/s) and 357 Magnum Jacketed Soft Point (JSP) bullets, with nominal masses of 10.2 g (158 gr) at a reference velocity of 436 m/s (1430 ft/s ± 30 ft/s). It also provides protection against the threats mentioned in [Types I and IIA].
1) The problems cited in the first post were due to network problems.
2) Headshots in PR are for the most part deadly, unless you're lucky.
3) Modern helmets will stop pistol ammunition and shrapnel 99% of the time, and sometimes rifle ammunition given special circumstances and, again, luck. Although helmets are primarily meant to stop shrapnel, having your head protected from small munitions is a comfortable feeling, and a comfortable soldier is a combat effective soldier. Whoever it was that said that most helmets won't stop a 9mm bullet, and even if they did, it would snap your neck, was, uh, misinformed.
4) I don't wanna get into the physics stuff. It's late and I'm hungry.
) . The bullet would penetrate the helmet and deform itself along with the helmet and possibly what is behind, in turn, dissipating a proportion (but not all) of it's forward kinetic energy as other forms. If the bullet keeps on going through and out the other end, the speed will be a whole lot less again.