The concept of a personal defense weapon is not a new one, starting in the early 80’s with FN’s P90. These are weapons that are intended for non-first-line troops. The first line troops being infantry etc. which are issued with full power rifles such as AR15’s, HK33’s, R4’s, Steyr AUG’s etc. Only about 20% of a military force are front-line troops that need such weapons. The rest of the force is made up of drivers, artillery, backup personnel and other non-combatants. For these personnel a full power rifle is not necessary and as such the concept of the personal defense weapon came into being. These weapons are small and compact weapons, smaller than an assault rifle but larger than a pistol, with ballistics better than a pistol or sub-machine gun.
Heckler & Koch’s entry into this field is a small, light and easy to handle weapon. They boast that it is easy to handle and operate due to the low recoil impulse of their new 4.6x30mm ammunition, which was developed in conjunction with Royal Ordnance, Radway Green in the U.K. They say that the weapon handles like a .22 and in automatic mode fires at a rate of 950 rounds per minute. The armour-piercing bullet is claimed to penetrate CRISAT protection, which is 1.6mm of titanium with 20 layers of Kevlar at 200m.
There is a great brochure by RUAG about the 4.6×30. This is the LINK