.300 Winchester Magnum

Know the exact name

At a glance

Cartridge family

Sporting & match rifle

Bullet specification

0.3090 in / 7.849 mmBullet maximum

Factory examples

30 loadsSelected, sourced examples below

Weight in cited examples

150–215 grGrains measure mass, not powder charge

.300 Winchester Magnum, commonly called .300 Win Mag, is a belted .30-caliber rifle cartridge. Its factory hunting and match examples are listed below.

Dimensions: open the exact dimensional drawing ↗. The displayed number is bullet maximum, rather than an assertion that every manufactured projectile or barrel has this exact diameter.

Origins & evolution

Background & development

Winchester introduced the .300 Winchester Magnum in 1963, after establishing its earlier .458, .338 and .264 magnum offerings. The new .30-caliber cartridge used a belted case with the shoulder positioned to provide substantial capacity while retaining compatibility with the general length of a conventional .30-06-class rifle action.

That rifle-package decision helped define its commercial appeal. It offered hunters a powerful .30-caliber option without requiring the longest magnum action, and it later developed a significant record in long-range target shooting as well. The familiar shortened name is .300 Win Mag. Its success also made it a reference point for later cartridges such as the .300 WSM, but those are different case designs. The .300 Win Mag’s history is the combination of Winchester’s 1960s sporting-magnum program, broad factory-rifle support and a later competitive life beyond its original hunting market.

Historical sources: Sierra: .300 Winchester Magnum cartridge history ↗

Construction changes the story

Loads, variations & specialty offerings

In the cited .300 Winchester Magnum examples, bullet weights are 150, 165, 175, 178, 180, 185, 190, 195, 200, 215 grains. These are the weights actually present in this source selection, not a claim that every possible loading is listed.

Bullet construction background: Hornady: anatomy of a bullet ↗. Exact product descriptions and velocities are cited in the factory table.

From the factory catalog

Explore the published data

Ballistics you can inspect

Select a legend entry to add or remove its line. Hover or tap a plotted point, or use the position slider. With the graph focused, arrow keys move the inspector. Solid dots identify source points; dashed connectors show estimates between them. Load construction, pressure category, and test setup can differ even at the same grain weight.

How to interpret the comparison

Changing bullet weight also often changes bullet design and propellant choice. Two curves are comparisons of the listed products, not a controlled experiment proving that bullet weight alone caused the difference. Catalog downrange points are projections under the maker’s conditions; barrel-study points are recorded observations in the study firearm.

Direct answers

Common questions

Keep exploring

Related references

Painted tips or polymer tips? Read the visual identification guide →

Browse the cartridge and gauge guides → · Return to the diameter comparison →

Trace the facts

Sources & methodology

Compiled by 2A Ledger from the linked standards, manufacturer publications, and identified test records. Checked October 18, 2026. Historical tests and older catalogs retain their original dates; a listing here does not establish current availability.

1. SAAMI: dimensional drawing · PDF p. 125 ↗
2. Sierra: .300 Winchester Magnum cartridge background ↗
3. Federal · PDF pp. 56–57 ↗
4. Federal · PDF pp. 58–59 ↗
5. Hornady · PDF p. 187 ↗
6. Federal · PDF pp. 52–53 ↗
7. Federal · PDF pp. 54–55 ↗

Diameter figures preserve the cited drawing convention. Inch–millimeter conversion uses exactly 25.4 mm per inch. Factory specifications describe the maker’s test setup; your firearm, ammunition lot, temperature, and measuring method can produce different results. This is an educational factory-ammunition reference, not a reloading manual.