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7-30 Waters
The 7-30 Waters cartridge was originally a wildcat cartridge developed by author Ken Waters in 1976 to give better performance to lever-action rifle shooters than the parent .30-30 Winchester cartridge, by providing a higher velocity and flatter trajectory with a smaller, lighter bullet. By 1984, Winchester introduced a Model 94 rifle chambered for the 7-30 Waters, establishing it as a commercial cartridge. In 1986, Thompson/Center began chambering 10-inch, 14-inch and 20-inch Contender barrels for the cartridge.
==Development==
Why neck down a .30 cal. cartridge to 7mm? This quote from a review of the 7-08 Rem. (a .308 Win. case necked down to 7mm), provides the answer.
There are two primary reasons a 7mm recoils less than an comparably effective .30 cal. cartridge: (1) to match the 7mm's ballistic coefficient requires a significantly heavier .30 cal bullet; and (2) to drive that heavier .30 cal bullet at similar velocities (for kinetic energy and wind resistance ("time-to-target")), requires more powder. This combination of heavier bullets with heavier powder charges significantly increases the recoil of the .30 caliber.
The .30-30 Winchester is typically limited to short ranges, primarily because of the relatively small case capacity and the 150-grain and 170-grain bullet weights. To compensate for this, Waters necked the cartridge down to use a 7mm bullet (.284 inches), rather than the original .308 caliber (7.62 mm) bullet. Because it was designed to function in lever-action rifles, the 7-30 maintained the same low working pressure, yet Waters' original design fired a lighter bullet (139 grains) at a higher velocity (2600 f/s).〔("7-30 Waters", retrieved 2013 May 04 )〕 A typical .30-30 factory load fires a 150-grain bullet at 2390 f/s, while the current 7-30 factory load fires a 120-grain bullet at 2700 f/s. Muzzle energy is just over 1900 ft-lbs for both of these loads, but the lighter weight 7mm bullet has a higher velocity and flatter trajectory.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「7-30 Waters」の詳細全文を読む
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