7-30 Waters

Type

Rifle and single shot handgun

Place of origin

United States

Production history

Designer

Ken Waters

Designed

1976

Produced

1984

Specifications

Parent case

.30-30 Winchester

Case type

Rimmed

Bullet diameter

.284" (7 mm)

Neck diameter

.306 in (7.8 mm)

Base diameter

.422 in (10.7 mm)

Rim diameter

.506 in (12.9 mm)

Rim thickness

.058 in (1.5 mm)

Case length

2.04 in (52 mm)

Overall length

2.52 in (64 mm)

Primer type

Large Rifle

Maximum CUP

40,000 CUP

Ballistic performance

Bullet mass/type	Velocity	Energy
120 gr (8 g) Nosler Partition FP	2,700 ft/s (820 m/s)	1,940 ft·lbf (2,630 J)
139 gr (9 g) Flat point	2,540 ft/s (770 m/s)	1,990 ft·lbf (2,700 J)
154 gr (10 g) Round nose	2,347 ft/s (715 m/s)	1,835 ft·lbf (2,488 J)

Test barrel length: 24"
Source(s): Cartridges of the World, 10th Ed., Barnes

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.

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.

Anything a 7mm can do, a .30 caliber of comparable sectional density and ballistic coefficient can also do. The catch is, in order to send a .30-caliber slug over a trajectory as flat as that 7mm bullet, about 20 percent more recoil is going to be generated. . . . [A bullet in] 7mm produces clearly superior downrange performance in terms of delivered energy and trajectory at any given recoil level [compared to a bullet in .30 caliber].

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). 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.

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Wikipedia