The .45 caliber bullet is not used in a sniper rifle.
Depends on the load
The L1A1 SLR used by the British military is in caliber 7.62 NATO, and has a muzzle velocity of about 2800 fps.
Depends on which .45- 45 Colt, 45 ACP, 45 Magnum, 45-70, and which bullet, and what it is fired from. If you mean the .45 ACP fired by a 1911A1 pistol, velocity varies from 830 FPS up to about 1020 fps. Slow, fat, but gets the job done.
The most basic answer is, a 9mm has a smaller diameter. Other differences, (in most cases) less muzzle energy, smaller and lighter bullet, higher velocity.
you will have to define if you mean commercial or wildcat.
800-1000 fps
The muzzle velocity of a .270 caliber rifle can vary depending on the specific ammunition being used. On average, a .270 Winchester round can have a muzzle velocity of around 3,000-3,200 feet per second. It's always best to check the specific manufacturer's data for the most accurate information.
It can vary from 900-1300 FPS depending on the weight and the firearm. Generally a smaller slug can have a greater velocity and a greater energy.
Caliber (for artillery) is the ratio of the barrel length to the bore diameter. So a 50 caliber 16" gun (Iowa-class) is longer than a 45 caliber gun (North Carolina-class), which gives a higher muzzle velocity, and therefore greater range and penetration.
http://www.michigan.org/Things-to-Do/Outdoors/Hunting/Default.aspx
Can't be answered without knowing the projectile weight and muzzle velocity