Hunting construction
Soft-point, bonded, partitioned, and monolithic expanding bullets are designed differently. Their intended impact-velocity ranges and use cases come from the bullet or ammunition manufacturer.
THE CARTRIDGE LIBRARY · SPORTING & MATCH RIFLE
.300 Remington Ultra Magnum
A large, beltless .30-caliber magnum, commonly shortened to .300 RUM. Its long case is a different design from the shorter Remington SAUM family.
2A Ledger reference desk · Sources checked October 18, 2026
Read the dimensions
- Overall · min–max
- 3.450–3.600 in
87.630–91.440 mm - Case length · max
- 2.850 in
72.390 mm - Bullet maximum
- 0.309 in
7.849 mm - Rim diameter · max
- 0.534 in
13.564 mm
Know the exact name
At a glance
- Cartridge family
- Sporting & match rifle
- Bullet specification
- 0.3090 in / 7.849 mmBullet maximum
- Factory examples
- 2 loadsSelected, sourced examples below
- Weight in cited examples
- 180–220 grGrains measure mass, not powder charge
.300 Remington Ultra Magnum is identified by its complete cartridge designation. The resource-table alternative is 300 Rem Ultra Mag. A caliber number, bullet diameter, or family resemblance on its own does not identify ammunition compatibility.
RUM and RSAUM/SAUM are separate cartridges. Keep the complete designation on ammunition and inventory records.
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
Remington introduced the .300 Remington Ultra Magnum in 1999. It was a conspicuous departure from the idea that a powerful American sporting magnum needed a belt. The design drew on the large .404 Jeffery case family, used a rebated rim, and located the cartridge by its shoulder rather than by a magnum belt.
The commercial aim was substantial .30-caliber performance in a full-size hunting rifle. That placed it at a different end of the market from the short-action magnums that attracted attention soon afterward. Remington later offered its separate Short Action Ultra Magnum family, but the original .300 RUM remained a large-capacity, long-action proposition. Its story marks a period in which major manufacturers revisited the architecture of the sporting magnum, with some seeking a smaller rifle package and others, like the RUM, seeking additional performance from a much larger case.
Historical sources: Sierra: .300 Remington Ultra Magnum cartridge history ↗
Construction changes the story
Loads, variations & specialty offerings
Match construction
Open-tip match and tipped match bullets prioritize consistency and aerodynamics. A match designation does not by itself mean the projectile was designed for hunting expansion.
Specialty offerings
Lead-free, reduced-recoil, and premium long-range products are separate load designs when offered. Compare the exact SKU, bullet weight, test barrel, and intended role rather than relying on a cartridge-wide average.
In the cited .300 Remington Ultra Magnum examples, bullet weights are 180, 220 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
180 grains
3,200 fps
CX®
220 grains
2,910 fps
ELD-X®
Compare all 2 cited factory load records
| Maker / product | Bullet mass | Published construction | Muzzle velocity | Test barrel | Source |
|---|---|---|---|---|---|
| Hornady82084 | 180 gr 11.66 g | CX® | 3,200 fps 975 m/s | Not stated here; see source | Hornady · PDF p. 187 ↗ |
| Hornady8209 | 220 gr 14.26 g | ELD-X® | 2,910 fps 887 m/s | Not stated here; see source | Hornady · PDF p. 187 ↗ |
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.
Read the original values as accessible tables
.300 Remington Ultra Magnum: factory velocity downrange
| Exact load | Source | Published points |
|---|---|---|
| 180 gr Hornady CX® | Hornady | 0: 3200; 100: 2988; 200: 2787; 300: 2594; 400: 2410; 500: 2233 |
| 220 gr Hornady ELD-X® | Hornady | 0: 2910; 100: 2766; 200: 2627; 300: 2492; 400: 2361; 500: 2234 |
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
What is .300 Remington Ultra Magnum?
A large, beltless .30-caliber magnum, commonly shortened to .300 RUM. Its long case is a different design from the shorter Remington SAUM family.
What diameter does .300 Remington Ultra Magnum use?
The cited dimensional standard lists 0.3090 inches (7.849 mm), bullet maximum. This drawing convention is different from a casual caliber nickname.
Are similarly named cartridges interchangeable?
RUM and RSAUM/SAUM are separate cartridges. Keep the complete designation on ammunition and inventory records.
Are the graph values measured or estimated?
The downrange view uses the exact manufacturer catalog records shown in the source table. Dashed connectors and intermediate inspector values use linear interpolation between the displayed source points. Calculated energy uses the listed bullet mass and velocity.
Does higher energy mean the best load?
Energy is calculated from mass and velocity. It does not establish accuracy, expansion, penetration, pattern density, recoil, or suitability for a particular firearm. Use the exact product documentation and firearm manual.
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.
- SAAMI: dimensional drawing · PDF p. 121 ↗
- Sierra: .300 Remington Ultra Magnum cartridge background ↗
- Hornady · PDF p. 187 ↗
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.