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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Why is .284 called a true 7mm?
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<blockquote data-quote="J E Custom" data-source="post: 1196827" data-attributes="member: 2736"><p>There are many cases of cartridges being named something different than actual size. Most are very close so they can be in a known category But the cartridge name can be misleading.</p><p></p><p>As far as I know this practice all started when Winchester wanted to produce a new cartridge In 7mm but did not want to call it that because the Chinese already had a 7mm And they wanted a "new" cartridge so they called it a 270 Winchester. It was a true 7mm but it had its own name</p><p>And would be different so it should sell. (It did).</p><p></p><p>So now it has become a standard practice to give a new cartridge a catchy name to improve sales.</p><p></p><p>The bullet used, is determined by the grove diameter not the bore diameter because some cartridges have slightly different bore diameters based on rifling height.</p><p></p><p>The 270 win has a bore diameter of .270 but the grove diameter is .277 making the rifling .0035</p><p>in height and requiring a bullet diameter of .277 to fit the grove/actual bore of the barrel.</p><p></p><p>A 284 Winchester has a bore diameter of .2755 and a grove diameter of .283 but the rifling height</p><p>is .00375. It requires a bullet diameter of .284. The .0005 difference is used when the bullet is engraved by the rifling.</p><p></p><p>This all sounds tricky but it is simple and trouble free as long as the correct bullet diameter for the grove diameter is used regardless what the cartridge is named. </p><p></p><p>Look at how many cartridges use the same bullet but have different names. Example; 5.56 Nato, 223 rem, 222 rem, 224 Weatherby, 22/250 etc. they all use the .224 diameter bullet.</p><p></p><p>NOTE: Even the Europeans don't stick to the actual dimensions even though they are on the Metric system and most of there 7mm's are actually .284.</p><p></p><p>J E CUSTOM</p></blockquote><p></p>
[QUOTE="J E Custom, post: 1196827, member: 2736"] There are many cases of cartridges being named something different than actual size. Most are very close so they can be in a known category But the cartridge name can be misleading. As far as I know this practice all started when Winchester wanted to produce a new cartridge In 7mm but did not want to call it that because the Chinese already had a 7mm And they wanted a "new" cartridge so they called it a 270 Winchester. It was a true 7mm but it had its own name And would be different so it should sell. (It did). So now it has become a standard practice to give a new cartridge a catchy name to improve sales. The bullet used, is determined by the grove diameter not the bore diameter because some cartridges have slightly different bore diameters based on rifling height. The 270 win has a bore diameter of .270 but the grove diameter is .277 making the rifling .0035 in height and requiring a bullet diameter of .277 to fit the grove/actual bore of the barrel. A 284 Winchester has a bore diameter of .2755 and a grove diameter of .283 but the rifling height is .00375. It requires a bullet diameter of .284. The .0005 difference is used when the bullet is engraved by the rifling. This all sounds tricky but it is simple and trouble free as long as the correct bullet diameter for the grove diameter is used regardless what the cartridge is named. Look at how many cartridges use the same bullet but have different names. Example; 5.56 Nato, 223 rem, 222 rem, 224 Weatherby, 22/250 etc. they all use the .224 diameter bullet. NOTE: Even the Europeans don't stick to the actual dimensions even though they are on the Metric system and most of there 7mm's are actually .284. J E CUSTOM [/QUOTE]
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Why is .284 called a true 7mm?
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