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1.
45
.45 Caliber cartridge. Sometimes used to refer to the firearms that fire such cartridges.
11.4mm in diameter, the average .45 caliber bullet weighs half an ounce.
Though there are many arcane .45 caliber cartridges, the two most common are the .45ACP (automatic Colt Pistol) and the .45 Colt, which is an obsolete but popular round. The .45 Colt round is longer than the .45ACP round, and was designed by Colt to fit their Single Action revolver, which the US Army used during the last decades of the nineteenth century. The .45ACP round was designed to be used in the 1911 pistol, by John Moses Browning. The gun was adopted by the US Army a few years after its creation, and was used by the United States until it was replaced by the Beretta M9 (Military designation for the Beretta 92) during the 1980s. Because it was used during both World Wars, Korea and Vietnam, hundreds of thousands of 1911s were produced. The Colt 1911 is often referred to as a “Colt .45” or “Government .45.” The pitfalls of the .45ACP cartridge are the large size of the bullet, heavy recoil and poor ballistics. Because the bullet is nearly 2.5 millimeters greater in diameter than the 9mm cartridge, far fewer can fit in a gun’s magazine, and the gun must be larger in order to accommodate the bullet. The heavy felt recoil is also a problem, because rapid or continued fire is difficult to maintain on target. The ballistics of the .45 caliber cartridge are also disappointing, the round travels nearly 200 feet per second slower than a 9x19 (9mm) cartridge. The 1911 pistol is still popular, despite being nearly 100 years old in design. The firearm’s single action mechanism and low magazine capacity have been overcome by some firearm manufacturers, most notably Para-Ordinance, whose LDA trigger systems are amazing, and whose high magazine capacity frames have revitalized the 1911 pistol.
If I don't get ya money yo 'gone catch a foty-five!
by Rob April 14, 2004
 
2.
45
1) a firearm chambered for the .45 ACP cartridge (usually a large frame semi-automatic) or the ammunition for same.
2) phonograph record or player with 45 RPM spindle speed.
3) (archaic) a firearm chambered for the .45 Colt cartridge (commonly a single-action revolver, as seen in western movies)
by Aantgray February 13, 2003
 
3.
45
.45 is the caliber, in inches, not mm. a 45mm gun is fucking huge.
Whoever thought a .45 is a 45mm is a moron.
by Anonymous February 11, 2003
 
4.
45
A phonograph record played at 45 RPM. It was about 8 inches across and had a very large central hole. It played a single song.
Peggy Sue has a whole box of Elvis 45s.
by Cap'n Bullmoose April 23, 2005
 
5.
4.5
Campus police, not quite the 5-0
Dude, is that the 5-0?
Nah, just 4.5, keep rollin
by Subeej March 31, 2003
 
6.
45
A hybrid left hook/uppercut, coined by Oscar De La Hoya due to the angle at which the punch is delivered.
“I just reached for my '45' and just like the Carter fight," De La Hoya delivered a “skin-shattering cut, this time over the left eye of my opponent."
by ChippL December 28, 2008
 
7.
45
A beer called Colt 45 & can be ordered at many convience stores
Hey Jamall grab me a 6 of 45!
by Damnit Janit May 13, 2007