.284 Winchester

.284 Winchester
.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
Bullet mass/type Velocity Energy 100 gr (6 g) HDY 100 HP 3,175 ft/s (968 m/s) 2,238 ft⋅lbf (3,034 J) 120 gr (8 g) SPR 120 SP 2,968 ft/s (905 m/s) 2,347 ft⋅lbf (3,182 J) 139 gr (9 g) HDY 139 SP 2,845 ft/s (867 m/s) 2,498 ft⋅lbf (3,387 J) 150 gr (10 g) Super-X Power-Point 2,860 ft/s (870 m/s) 2,724 ft⋅lbf (3,693 J)
Test barrel length: 24 in (610 mm) Source(s): Winchester Ammunition Accurate Powder [1]

The .284 Winchester (7.21x55mmRB) is a rebated rim rifle cartridge introduced by the Winchester Repeating Arms Company in 1963.

The .284 Winchester was designed to duplicate the performance of the .270 Winchester and .280 Remington cartridges from the new Winchester Model 100 autoloader and Winchester Model 88 lever-action rifles. The result was a 7 mm cartridge of comparable overall length to the .308 Winchester with greater case capacity and power potential.

.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.^[2]