5.56x45mm is the ammunition used in the majority of the weapons available in Urban Terror. It is a small caliber, high velocity round. The cartridge pictured above is made by Winchester and has a 55 gr. bullet, a muzzle velocity of 3270 fps and muzzle energy of 1305 ft-lbs. It is best suited for closer combat ranges (under 400 meters), and is prefered for its compact size and light weight, reducing the burden of carrying ammunition. Wounds inflicted by this round are less likely to be fatal because of the bullet's light weight and tendancy to fragment.

This cartridge has similar dimensions as a .223 Remington, the main differences being at the throat of the chamber. These slight differences can cause excessive chamber pressure when firing .223 ammunition in a military chamber and poor performance when firing NATO ammunition in a SAAMI specification chamber. SAAMI specifications for commercial .223 ammunition has a smaller diameter bullet seat, a shorter throat and less free bore, and these differences can cause chamber pressure to be as much as 10,000 PSI higher. 5.56mm ammunition should not be fired in a rifle chambered for .223 unless the manufacturer explicitly states it can also handle 5.56mm NATO ammunition.

The 7.62x39mm cartridge is used in the AK-103. It is the most common military small arms ammunition in Asian and Middle Eastern regions because of its use in AK-47 and SKS assault weapons. The Soviets believe the 7.62mm bullet is superior because it offers more "punch". This one is made by Winchester. It has a 123 gr. bullet, a muzzle velocity of 2355 fps and a muzzle energy of 1509 ft-lbs.

The 7.62x51mm cartridge used in the H&K PSG-1, which is said to be the world's most accurate semi-automatic rifle. This round is the most commonly used short-range sniper cartridge, having an effective range of about 1000 meters.

This round has similar but not identical dimensions as a .308 Winchester. The chamber for a 7.62mm NATO cartridge is slightly longer, but most manufacturers of 7.62mm NATO conform to the headspace limitations of a .308 Winchester chamber. .308 Winchester also has a chamber pressure about 12,000 PSI higher, so it should never be used in a firearm chambered for 7.62mm NATO unless it explicitly states that it can handle .308 Winchester as well.

9mm is used in the H&K MP-5 submachine gun and also the Beretta sidearm. The Winchester cartridge shown is a round-nose target round with a 115 gr. bullet, a muzzle velocity of 1190 fps and muzzle energy of 362 ft-lbs. However, one might expect a heavier hollow-point round in live combat situations. I load my Ruger with Federal 135 gr Hydra-Shok jacketed hollow points, which have a muzzle velocity of 1050 fps and energy of 330 ft-lbs.

.45 ACP is used in the UMP submachine gun. Normally a handgun ammunition, .45 has been around for over a hundred years and has been used for a long time in the standard military sidearm, the Colt M-1911. It has a large, heavy bullet, but it has very low velocity. .45 is the only ammunition in the game to leave the muzzle at less than the speed of sound.

The .338 Lapua Magnum (aka 8.58x71mm) is a bad-ass round. Designed specifically for sniping, it is cable of penetrating up to five layers of body armor at 1200 meters or 15mm (over half an inch) of amor steel plate at 500 meters. Its effective range is about 1600 meters (one mile). It has a large 250 gr. bullet, which leaves the muzzle at 2970 fps yielding an incredible 4896 ft-lbs of energy. A bit of information about the round can be found here.

The .338 Lapua Magnum is used in the Remington SR-8. In the game, a hit anywhere on the head or torso will result in a kill, kevlar body armor being completely ineffective against this round.