you will have to define if you mean commercial or wildcat.
The .45 caliber bullet is not used in a sniper rifle.
The L1A1 SLR used by the British military is in caliber 7.62 NATO, and has a muzzle velocity of about 2800 fps.
The .223 Remington rifle cartridge has a muzzle velocity of approximately 3600 feet per second.
Some of the fastest- the Ruger .204, the .220 Swift, and the 30-06- but only if the 30-06 is shooting the Remington Accelerator. That is a sabot cartridge that fires a small .25 caliber bullet at roughly 4,500 fps.
No one answer. There are dozens of different .44 caliber cartridges, and hundreds of different loadings of those cartridges. A rifle will have a different velocity than a handgun. This is sort of like "how fast can a V8 car go?"
muzzle velocity
300m/s
Among standard rifle cartridges the Winchester .220 Swift is the velocity standard bearer. It clocks in at 4,000 ft/s (1,200 m/s). Rifles chambered in the caliber tend to have shorter-than-usual barrel lives. Among standard pistol cartridges the Smith and Wesson .460 is the current record holder at 2330 ft/s.
Muzzle velocity of the SS-109 cartridge is about 3100 feet per second.
The M4A1 version of the M16 rifle has a muzzle velocity of about 2900 feet per second, firing the 5.56mm cartridge.
Varies with barrel and cartridge, but the muzzle velocity is about 2600 feet per second.
a bullet of the same caliber and same grains of powder fired from a long barrel will have a higher muzzle velocity than if fired from a short barrel.