What determines how far a gun, specifically a rifle can shoot?
whats the difference between military rifles and something you could buy at a local gun shop. Any info greatly appreciated.
Two things will control how far the bullet will fly, velocity and ballistic coefficient.
The first is easy to understand, it is how fast the bullet leaves the muzzle. A ball thrown fast goes father than one thrown slow.
The second item is a little rougher to explain. It has to do with the weight of the bullet and the wind resistance of it’s shape. Bullets come in a wide range of shapes and some are better at going through the air than others. To use some technical terms, a spitzer boat tail will fly much father than a full wad-cutter. The spitzer boat tail has a long sharp nose, and a tapered base, the wad-cutter is flat on the front. The air flows around the spitzer bullet, and develops a shock-wave in front of the wad-cutter. If you have ever rowed a boat across the water, it is easier to move the rounded bow through the water the the flat stern.
http://en.wikipedia.org/wiki/Bullet
Now as to your second question, the only real difference between the military rifles and what can be purchased at your local gun shop is what is known as selective fire. Virtually all military rifles today have some variant of full automatic fire, which is not readily available on the civilian market. Other than that, if you want a semi auto gun that looks like one of the military guns, they are available in most states.
Having said that, if you want to have a selective fire gun, they are available, but the process takes time and a great deal of money. You need some very specific permission from the local, county, state and federal governments, with lots and lots of paperwork that must be approved. You will have to have an extensive background check.
Since you seem interested in firearms, try the NRA site and these others.
http://www.nra.org/
http://www.gunbroker.com/
http://www.reenactor.net/forums/index.php?page=17
http://www.milwarehouse.com/wwii_reenacting_sources.htm
577 t-rex rifle shots (aka elephant gun)