In some says, the new Army pistol is very similar to the old one. It's assumed the standard issue version will fire the 9mm Luger round which was also standard in the M9 and across many NATO military pistols. Standard magazines are available with a capacity of 17-22 rounds, only slightly more than the 15 rounds magazines standard on the M9. In terms of the type of round it fires and the speed at which it can fire, there's no real difference between the pistols.
However, in another sense the P320 (its military designation has not yet been announced, though the procurement program under which it was selected was called the MHS: Modular Handgun System) is a much more modern type of firearm, bringing to handguns the same features which have made the M4 Carbine the basis for one of the most popular rifle/carbine designs in the world.
Sig Sauer designed the P320 around a polymer frame. This makes it lighter than an all-metal pistol such as the M9 or the M1911. When soldiers are already carrying a lot of gear, having a pistol that weights ten ounces less is an advantage. However, polymer framed pistols (most famously the Glock pistols which are carried by many police forces) have been around for a long time. (Contrary to myth, polymer frames were adopted for handguns because they're lighter, they present no advantage in hiding from metal detectors because other parts of the gun are still metal.) What is different about the P320 is that it is a completely modular handgun. This is what the Fire Control Unit (the central mechanism of the gun which carries the serial number and thus is considered by the ATF to be the legal gun) looks like:
|P320 Fire Control Unit|
That fire control unit forms the functioning core of the pistol. It goes into the polymer frame, and the barrel, slide, etc. fit around it. The pistol is designed so that a non-gunsmith can take it apart and put it together again in minutes without needing any tools.
Because all the parts which define the frame size, the barrel length, even the caliber of the pistol are modular parts which connect to the universal fire control system, this means that if the owner (whether a gun enthusiast or a company armorer) owns a full range of modular parts, in minutes he can change the one gun from a small framed sub-compact which could fit in a pocket to a large framed full size pistol. He can even switch calibers from 9mm to .45 Auto or .40 S&W.
|Sig Sauer modular parts for P320|
This is a huge advantage for the army, in which adding another gun means stocking all the parts to repair and maintain it. If a special operations force wanted to carry .45 pistols, an armorer would have had to support some entirely different gun (Beretta makes .45 pistols, but special ops teams often carry an M1911 or a Glock) for their needs. If some personnel wanted a pistol which was smaller and lighter, that too would have to be an entirely different pistol. With the P320 modular system, however, an armorer could simply swap out a few parts and support a wide variety of needs. In this respect, the new modular handgun system will be very much on a par with the lego-like customizability which has made the civilian AR-15 version of the M16/M4 system so popular.
|Beretta M9 9mm Service Pistol|