loaded with steel shot causing barrel wear has not been published and the US equivalent of CIP, SAAMI, does not have any such restrictive limitations on the velocity of commercial steel shotshells sold in the United States. Similarly, shotgun manufacturers selling shotguns in the United States select their own appropriate standards for setting steel hardness for shotgun barrels and for velocities of steel shotshell loaded ammunition. Some indoor shooting ranges prohibit the use of steel shot over concern of it causing a spark when hitting an object down range and causing a fire. Shot sizes Shotshells are loaded with different sizes of shot depending on the target. For skeet shooting, a small shot such as a No.8 or No.9 would be used, because range is short and a high density pattern is desirable. Trap shooting requires longer shots, and so a larger shot, usually #7½ is used. For hunting game, the range and penetration needed to assure a clean kill is considered. Shot loses its velocity very quickly due to its low sectional density and ballistic coefficient (see external ballistics). Small shot, like that used for skeet and trap, will have lost all appreciable energy by around , which is why trap and skeet ranges can be located in relatively close proximity to inhabited areas with negligible risk of injury to those outside the range. Birdshot Birdshots are designed to be used for waterfowl and upland hunting, where the game is agile small/medium-sized birds. Their sizes are numbered similar to the shotgun gauges—the smaller the number, the larger the shot (except in the obsolete Swedish system, in which it is reversed). Generally birdshot is just called "shot", such as "number 9 shot" or "BB shot". There are small differences in size of American, Standard (European), Belgian, Italian, Norwegian, Spanish, Swedish, British, and Australian shot to make matters more complex. That is because some systems go by diameter in inches (American), some go by diameter in millimeters (European), and the British system goes by the number of lead shot per ounce. Australia has a hybrid system due to its market being flooded with a mixture of British, American, and European shells. For American shot, a useful method for remembering the diameter of numbered shot in inches is simply to subtract the shot size from 17. The resulting answer is the diameter of the shot in hundredths of an inch. For example,