The 338 Remington Ultra Magnum is a centerfire rifle cartridge standardised by SAAMI in ANSI/SAAMI Z299.4. SAAMI sets its maximum average pressure at 65,000 psi, and measures its reference velocities in a 24.000 in standard test barrel rifled 1 turn in 10.00 in. This guide sets out SAAMI’s published reference velocity for each bullet weight, computes the muzzle energy each one carries, and compares the 338 Remington Ultra Magnum with the 338 Lapua Magnum on the same basis.
338 RUM ballistics chart: SAAMI reference data
SAAMI publishes one nominal mean instrumental velocity for each reference bullet weight, measured at 15 feet from the standard test barrel. It does not publish energy, so the ft-lb column is computed. Where SAAMI lists more than one velocity for a weight, both ends of the span are shown.
Scroll the table sideways for the remaining columns.
| Bullet weight | Reference velocity | Computed muzzle energy |
|---|---|---|
| 250 gr | 2,850 fps | 4,508 ft-lb |
What the numbers mean for a shot
SAAMI lists a single reference bullet weight for the 338 Remington Ultra Magnum: 250 grains, listed at 2,850 fps, which computes to 4,508 ft-lb. SAAMI publishes no other weight for it, so the table has one row. For any other bullet weight, use the figures the maker publishes for that item.
None of this is a downrange figure. SAAMI measures at 15 feet, so retained velocity, energy and drop depend on the bullet’s ballistic coefficient, which SAAMI does not publish. Each product in our 338 RUM ammo range lists whatever its maker publishes for that item.
Twist rate, chamber and pressure
SAAMI’s standard test barrel for the 338 Remington Ultra Magnum is 24.000 in long and rifled 1 turn in 10.00 in, with a .338 in groove diameter. That is the barrel every reference velocity above was measured in, not a statement about your rifle: a shorter production barrel will usually give lower velocity, and a twist slower than a bullet needs will not stabilise it. The maximum average pressure is 65,000 psi. Fire 338 Remington Ultra Magnum ammunition only in a firearm chambered for it. Several unrelated cartridges share a number, so match the full designation on the box to the marking on your barrel.
338 RUM vs 338 Lapua: the SAAMI comparison
A figure from one maker’s catalogue cannot be laid beside a figure from another’s: each picks its own test barrel, zero and bullet, and many publish no test barrel at all. SAAMI is the shared basis, because it fixes one standard test barrel and one way of measuring velocity for every cartridge it lists.
Scroll the table sideways for the remaining columns.
| SAAMI specification | 338 Remington Ultra Magnum | 338 Lapua Magnum |
|---|---|---|
| Maximum average pressure | 65,000 psi | 65,000 psi |
| Standard test barrel length | 24.000 in | 24.000 in |
| Test barrel twist rate | 1 turn in 10.00 in | 1 turn in 10.00 in |
| Test barrel groove diameter | .338 in | .338 in |
| Lightest reference load | 250 gr — 2,850 fps / 4,508 ft-lb | 250 gr — 2,950 fps / 4,830 ft-lb |
| Heaviest reference load | 250 gr — 2,850 fps / 4,508 ft-lb | 300 gr — 2,620 fps / 4,572 ft-lb |
The 338 Remington Ultra Magnum and the 338 Lapua Magnum share the same maximum average pressure, 65,000 psi. At 250 grains, a weight both list, SAAMI’s 338 Remington Ultra Magnum reference velocity is 2,850 fps (4,508 ft-lb computed), against 2,950 fps (4,830 ft-lb) for the 338 Lapua Magnum. On that row the 338 Lapua Magnum carries the more energy.
What SAAMI cannot settle is anything past the muzzle. It publishes no ballistic coefficients and no downrange data, so it cannot say which cartridge shoots flatter at distance; that depends on the bullet. We stock the other side of this comparison too: 338 Lapua ammo.
338 RUM ballistics questions
What is the maximum pressure of the 338 Remington Ultra Magnum?
ANSI/SAAMI Z299.4 sets the maximum average pressure for the 338 Remington Ultra Magnum at 65,000 psi.
What twist rate and barrel length does SAAMI use for the 338 Remington Ultra Magnum?
SAAMI’s standard test barrel for the 338 Remington Ultra Magnum is 24.000 in long and rifled 1 turn in 10.00 in. Your own rifle may differ.
Is the 338 Remington Ultra Magnum more powerful than the 338 Lapua Magnum?
Power is not a SAAMI measure, but reference muzzle energy is a fair proxy. At 250 grains, a weight both list, SAAMI’s 338 Remington Ultra Magnum reference velocity is 2,850 fps (4,508 ft-lb computed), against 2,950 fps (4,830 ft-lb) for the 338 Lapua Magnum.
What is the effective range of the 338 Remington Ultra Magnum?
Effective range is not a SAAMI specification and it is not a measured figure. SAAMI measures velocity at 15 feet, so it says nothing about performance at distance; that depends on the bullet and the shooter.
How much does the 338 Remington Ultra Magnum drop at 300 yards?
SAAMI publishes muzzle velocity only, so it cannot give a drop figure. Drop depends on the bullet’s ballistic coefficient and on the zero range. A drop figure is unusable without its zero, so use the figure a maker prints for the specific load.
Where to buy these loads
Hilltop Armory carries 338 RUM ammunition from Nosler and Federal. Browse the full 338 RUM ammo range.
