The 338 Weatherby Rebated Precision Magnum is a centerfire rifle cartridge standardised by SAAMI in ANSI/SAAMI Z299.4. SAAMI sets its maximum average pressure at 65,000 psi. This guide sets out SAAMI’s published reference velocity for each bullet weight, computes the muzzle energy each one carries, and compares the 338 Weatherby Rebated Precision Magnum with the 338 Winchester Magnum on the same basis.
338 Weatherby RPM 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 |
|---|---|---|
| 225 gr | 2,800 fps | 3,916 ft-lb |
What the numbers mean for a shot
SAAMI lists a single reference bullet weight for the 338 Weatherby Rebated Precision Magnum: 225 grains, listed at 2,800 fps, which computes to 3,916 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 Weatherby RPM ammo range lists whatever its maker publishes for that item.
Twist rate, chamber and pressure
The maximum average pressure is 65,000 psi. Fire 338 Weatherby Rebated Precision 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 Weatherby RPM vs 338 Win Mag: 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 Weatherby Rebated Precision Magnum | 338 Winchester Magnum |
|---|---|---|
| Maximum average pressure | 65,000 psi | 64,000 psi |
| Standard test barrel length | Not read from the drawing | 24.000 in |
| Test barrel twist rate | Not read from the drawing | 1 turn in 10.00 in |
| Test barrel groove diameter | Not read from the drawing | .338 in |
| Lightest reference load | 225 gr — 2,800 fps / 3,916 ft-lb | 185 gr — 3,075 fps / 3,884 ft-lb |
| A weight both list | 225 gr — 2,800 fps / 3,916 ft-lb | 225 gr — 2,770–2,950 fps / 3,833–4,347 ft-lb |
| Heaviest reference load | 225 gr — 2,800 fps / 3,916 ft-lb | 300 gr — 2,415 fps / 3,884 ft-lb |
SAAMI standardises the 338 Weatherby Rebated Precision Magnum at 65,000 psi and the 338 Winchester Magnum at 64,000 psi, so the 338 Weatherby Rebated Precision Magnum runs 1,000 psi higher. At 225 grains, a weight both list, SAAMI’s 338 Weatherby Rebated Precision Magnum reference velocity is 2,800 fps (3,916 ft-lb computed), against up to 2,950 fps (4,347 ft-lb) for the 338 Winchester Magnum. On that row the 338 Winchester 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 Win Mag ammo.
338 Weatherby RPM ballistics questions
What is the maximum pressure of the 338 Weatherby Rebated Precision Magnum?
ANSI/SAAMI Z299.4 sets the maximum average pressure for the 338 Weatherby Rebated Precision Magnum at 65,000 psi.
Is the 338 Weatherby Rebated Precision Magnum more powerful than the 338 Winchester Magnum?
Power is not a SAAMI measure, but reference muzzle energy is a fair proxy. At 225 grains, a weight both list, SAAMI’s 338 Weatherby Rebated Precision Magnum reference velocity is 2,800 fps (3,916 ft-lb computed), against up to 2,950 fps (4,347 ft-lb) for the 338 Winchester Magnum.
What is the effective range of the 338 Weatherby Rebated Precision 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 Weatherby Rebated Precision 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 Weatherby RPM ammunition from Weatherby. Browse the full 338 Weatherby RPM ammo range.
