.284 Winchester
The .284 Winchester (7.21x55mmRB) is a rebated rim firearm cartridge, introduced by Winchester in 1963.
| .284 Winchester | ||||||||||||||||||||
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.284 Winchester (center) with .308 Win (left) and 7mm Remington Magnum (right) | ||||||||||||||||||||
| Type | Rifle | |||||||||||||||||||
| Place of origin | United States | |||||||||||||||||||
| Production history | ||||||||||||||||||||
| Designer | Winchester | |||||||||||||||||||
| Designed | 1963 | |||||||||||||||||||
| Manufacturer | Winchester | |||||||||||||||||||
| Produced | 1963–present | |||||||||||||||||||
| Specifications | ||||||||||||||||||||
| Case type | rebated rim, bottleneck | |||||||||||||||||||
| Bullet diameter | 7.21 mm (0.284 in) | |||||||||||||||||||
| Land diameter | 7.00 mm (0.276 in) | |||||||||||||||||||
| Neck diameter | 8.13 mm (0.320 in) | |||||||||||||||||||
| Shoulder diameter | 12.06 mm (0.475 in) | |||||||||||||||||||
| Base diameter | 12.72 mm (0.501 in) | |||||||||||||||||||
| Rim diameter | 12.01 mm (0.473 in) | |||||||||||||||||||
| Rim thickness | 1.37 mm (0.054 in) | |||||||||||||||||||
| Case length | 55.12 mm (2.170 in) | |||||||||||||||||||
| Overall length | 71.12 mm (2.800 in) | |||||||||||||||||||
| Case capacity | 4.29 cm3 (66.2 gr H2O) | |||||||||||||||||||
| Rifling twist | 254 mm (1 in 10 in) | |||||||||||||||||||
| Primer type | Large rifle | |||||||||||||||||||
| Maximum pressure (C.I.P.) | 440.00 MPa (63,817 psi) | |||||||||||||||||||
| Maximum pressure (SAAMI) | 386 MPa (56,000 psi) | |||||||||||||||||||
| Ballistic performance | ||||||||||||||||||||
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| Test barrel length: 24 in (610 mm) Source(s): Winchester Ammunition Accurate Powder | ||||||||||||||||||||
The .284 Winchester was designed to achieve .270 Winchester and .280 Remington performance from the new Winchester Model 100 autoloader and Winchester Model 88 lever-action rifles. The result was a 7 mm cartridge with about the same overall length as the .308 Winchester but with a wider body, that yields a powder capacity about the same as that of the .270 Winchester and .280 Remington.
.284 Winchester has enjoyed a resurgence due to interest from long-range competitive shooters. Winchester has continued to produce brass cases for this cartridge since 1963.
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