That depends. Rifle, shotgun, pistol, cannon, pellet gun, or airsoft? The 16" guns on a battleship can fire a one ton shell about 26 miles, but they are not "on the market". For rifles, the .50 BMG is close to the upper limit. Shotguns- the 10 g 3.5" magnum, and handgun is a tossup- .500 S&W being in the upper ranks, although there are many handguns in rifle calibers (even one in .600 Nitro Express, and one in .50 BMG)
For rifles, it's probablly the Russian PTRS anti-tank rifle. The 14.5 x 114mm cartridge fires a 65.5 gram bullet at 3200 feet per second- far more energcy than the .50 Barrett, or elephant guns such as the .600 Nitro Express or .460 Weatherby magnum.
"Gun" has various meanings. Artillery pieces are referred to as "guns", as are battleship deck guns.
As far as individual, man portable weapons go, which are intended to be operated by one person, the Croatian RT-20 and South African Denel NTW-20x110 would be your likely answers. Both are anti-materiel sniping weapons designed to fire a 20x110mm cartridge developed for the Hispano-Suiza antiaircraft cannons.
Factory, I'd probably say the 500 Magnum
If you are referring to the present, today's most powerful sub-machine gun is the H&K UMP .45 cal sub-machine gun, or the Kriss Vector SMG. if you are referring to the past however then its undeniably the Tommy Gun. also a .45 cal sub-machine gun.
The worlds most powerful destroyer is the Sejong the Great class destroyer. These ships are operated by the Republic of Korea Navy. There are three in the current fleet with each having a capacity for 400 crew members. The weapons each ship is equipped with are 16 anti-ship missiles, 6 torpedoes, 3 cruise missiles, helicopters and a 1.5 inch naval gun.
Gun wise, was an Iowa class battleship. Most powerful (regardless of guns) was an aircraft carrier, most likely an Essex or Midway class during the war. The USS Enterprise was the most decorated USN warship of WWII, but was a Yorktown class carrier. *It was the "Constitution"*
Rifle, shotgun, or handgun? The 10 gauge shotgun at close range would be very high on the list, as would some of the buffalo rifle cartridges, such as the 45-110. The .45 Colt revolver was possibly the most powerful handgun of the day.
My guess is the M1917 Browning machine gun in 30/06
The AK-47 is the most lethal gun because you can learn how to use it in one hour or less. It is also the most produced weapon in the world.
Factory, I'd probably say the 500 Magnum
Other than a toy gun or water gun, the next most powerful one a citizen can have without a permit is a "B.B. gun".
The IS-2 and IS-3 "Josef Stalin". They boasted a 122mm main gun, and remained the most powerful tanks in the world for almost 20 years after the end of the war.
Not even close. There are several more powerful handgun cartridges, not counting the single shot pistols that use rifle cartridges. While Dirty Harry may have proclaimed it to be "The most powerful handgun in the world"- it is not.
50 cal. machine gun. i don't know who decided to use it.
577 T Rex
star cannon
The magnum .55 is the most powerful, but some Desert Eagle has the highest calibre bullet.
light machine gun is the m249 a medium machine gun is the m240 and the heavy machine gun is the browning m2 50. cal machine gun
10 gauge shotgun