Body armor on the battlefield...may soon be challenged by a new breed of armor-piercing bullets. Over the last few year Russia...has developed and marketed several different types of armor-piercing rifle rounds that are specifically designed to penetrate high-quality body armor. The secret of the new ammunition’s penetration power is...the material that is used to produce the bullet’s core. The ammunition developers have been using a number of different materials, including steel, tungsten, and even uranium alloys. ... A good example ...includes the ***7N10 Armor-Piercing Round***, in 5.45x39, which is capable of penetrating a steel slab 16mm thick from 100 meters. The 5.45mm is the round used in the AK-74, the standard infantry weapon in Russia [which include the ubquitous AK-47].
Another round known as the ***7N13***, chambered for 7.62x54R, is especially effective when fired from the Dragunov SVD sniper rifle. Armor penetration is the same as the 7N10 at 100 meters. Originally these bullets were designed to be used against both armored infantry and light armored vehicles, and test firings have proven that many of these rounds are quite effective at piercing the armor on BTRs and BMPs (which are about 5 and 10mm thick). However, the results against Western-style armored vehicles are not known since Western vehicles have not been used as test subjects, nor have they been encountered in combat. One thing is certain, though, any hostile force with access to this ammunition would make life extremely difficult for troops wearing even high-quality body armor like the Interceptor. Most small arms still in production by the Russian Federation have some sort of armor-piercing ammunition made for them. The Russians have hinted that they might try to issue the new ammunition to regular soldiers and not just special forces.
In the US and Western Europe, similar developments are underway since developed militaries are finally beginning to realize that their military forces’ (especially infantry) may have a high chance of encountering hostile forces equipped with body armor. One of the best innovations in small arms, as far as armor-piercing ammunition is concerned, is the Heckler & Koch MP7 rifle. ... In addition to its compact size and light weight, the weapon is unique is that it is specifically designed to penetrate body armor. H & K specifically designed the specialty ammunition to penetrate Russian body armor, since this has become the NATO standard target when developing armor penetrating ammunition. ...
[But] Russia currently markets a wide range of body armor, called the KIRASA series, whose protection levels vary from very low to very high. The lowest form of KIRASA armor incorporates Level I protection, which guards against pistol ammunition from .22LR to .38 caliber. The highest form of KIRASA body armor, and the one that NATO should be most worried about, is the KIRASA-D Model I. This KIRASA-D is a ballistic vest intended for ground troops that incorporates ceramic plates on the torso section that raise its protection level to Level IV (the same as the US military’s Interceptor). The problem with this is Russia has a history of selling weapons to whomever can pay for them and the potential for these vests to fall into the hands of potential enemies is no small matter. Unless NATO develops ammunition to penetrate Level IV vests in the future, it may have a serious problem on its hands in a potential conflict. The AK-74 is widely distributed is the Former Soviet Union and is used by a number of insurgent groups, especially the ones in Chechnya (who constitute one of the most well-equipped insurgent groups in the world) and US troops is very likely to encounter it in the hands of enemy troops in a future conflict. The MP7 has less of a chance of being encountered by US troops, but the possibility that it could fall into hostile hands, like the MP5, is very real.
I believe that this is the reason the US is developing a .280 caliber round.