The Lorcin .380 is the #1 contender on the BATFE's list for several years. Smaller "pocket pistols", such as the .22, .25, and .32 also tend to be popular.
The caliber is .68, probably the most common caliber for paintballs.
The most common hand-gun caliber used to be 9mm Luger. Recently I bought a pistol and took a self-defense course. Now it seems the most popular caliber is the.40 Caliber Smith and Wesson.********There are popular, and there are most common. The most common gun caliber is .22 rimfire, in terms of the total number sold.
22 lr
One of the most common ninja weapons is the ninja star.
Guns are the most common murder weapon in the United States. Handguns of 22 caliber and 38 caliber are most used.
My best guess would be a Russian M1895 Nagant pistol 7.62 caliber. It would have been the most common pistol available in Russia at that time.
Firearms
.69 caliber Springfield
Not in the current U.S. military. the most common handgun caliber currently is the 9mm.
Winchester 94 in 30-30 caliber.
The weapons were a k47s and rpgs. most common the rpd or m4 carbine.
The most common weapons that were used by (ancient) Greek soldiers were the spear and the sword.