The 340 Weatherby Magnum is a centerfire rifle cartridge standardised by SAAMI in ANSI/SAAMI Z299.4. SAAMI sets its maximum average pressure at 62,500 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 340 Weatherby Magnum with the 338 Lapua Magnum on the same basis.
340 Weatherby Magnum 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 |
|---|---|---|
| 200 gr | 3,210 fps | 4,575 ft-lb |
| 210 gr | 3,200 fps | 4,774 ft-lb |
| 225 gr | 2,860 fps | 4,086 ft-lb |
| 250 gr | 2,950 fps | 4,830 ft-lb |
What the numbers mean for a shot
SAAMI lists 4 reference bullet weights for the 340 Weatherby Magnum, from 200 to 250 grains. The lightest, 200 grains, is listed at 3,210 fps, which computes to 4,575 ft-lb. The heaviest, 250 grains, is listed at 2,950 fps, or 4,830 ft-lb.
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 340 Weatherby Magnum ammo range lists whatever its maker publishes for that item.
Twist rate, chamber and pressure
SAAMI’s standard test barrel for the 340 Weatherby 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 62,500 psi. Fire 340 Weatherby 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.
340 Weatherby Magnum 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 | 340 Weatherby Magnum | 338 Lapua Magnum |
|---|---|---|
| Maximum average pressure | 62,500 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 | 200 gr — 3,210 fps / 4,575 ft-lb | 250 gr — 2,950 fps / 4,830 ft-lb |
| A weight both list | 250 gr — 2,950 fps / 4,830 ft-lb | 250 gr — 2,950 fps / 4,830 ft-lb |
| Heaviest reference load | 250 gr — 2,950 fps / 4,830 ft-lb | 300 gr — 2,620 fps / 4,572 ft-lb |
SAAMI standardises the 340 Weatherby Magnum at 62,500 psi and the 338 Lapua Magnum at 65,000 psi, so the 340 Weatherby Magnum runs 2,500 psi lower. At 250 grains, a weight both list, SAAMI’s 340 Weatherby Magnum reference load is 2,950 fps and 4,830 ft-lb computed, against 2,950 fps and 4,830 ft-lb for the 338 Lapua Magnum. On that row the 340 Weatherby 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.
340 Weatherby Magnum ballistics questions
What is the maximum pressure of the 340 Weatherby Magnum?
ANSI/SAAMI Z299.4 sets the maximum average pressure for the 340 Weatherby Magnum at 62,500 psi.
What twist rate and barrel length does SAAMI use for the 340 Weatherby Magnum?
SAAMI’s standard test barrel for the 340 Weatherby Magnum is 24.000 in long and rifled 1 turn in 10.00 in. Your own rifle may differ, and a twist slower than a long, heavy bullet needs will not stabilise it.
What bullet weights does SAAMI list for the 340 Weatherby Magnum?
SAAMI lists 4 reference weights, from 200 to 250 grains: 200, 210, 225 and 250.
Is the 340 Weatherby 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 340 Weatherby Magnum reference load is 2,950 fps and 4,830 ft-lb computed, against 2,950 fps and 4,830 ft-lb for the 338 Lapua Magnum.
How much does the 340 Weatherby 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.
What is the effective range of the 340 Weatherby 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.
Where to buy these loads
Hilltop Armory carries 340 Weatherby Magnum ammunition from Nosler, Weatherby, CorBon and Norma. Browse the full 340 Weatherby Magnum ammo range.
