Last reviewed: 2026-04-18 by Jake Terry, FFL07/SOT3, NRA-certified firearms instructor.
357 Magnum Xtreme Penetrator ammunition from Underwood pairs flash-suppressed propellants with Lehigh Defense’s CNC-machined solid-copper projectile to deliver deep, straight penetration through intermediate barriers. Loaded to 1550 feet per second at the muzzle from a 6-inch test barrel, the 140-grain fluted bullet produces 747 foot-pounds of energy and maintains momentum through auto glass, drywall, and heavy clothing. Nickel-plated brass cases resist corrosion during carry and reload cleanly when you process spent brass. The blunt nose feeds reliably in revolver cylinders and tubular magazines, making this a proven choice for defensive revolver loads and lever-action carbine applications where barrier penetration is a priority.
Load Profile
Underwood engineers this round around Lehigh Defense’s Xtreme Penetrator design — a solid-copper bullet with radial flutes that channel fluid away from the nose, creating hydraulic pressure spikes as the projectile advances. The fluted geometry maintains straight-line travel through barriers that deform conventional hollow-points, and the copper construction eliminates lead exposure during indoor range sessions. Flash-suppressed powder preserves night vision when you fire in dim conditions, and boxer primers allow full reloadability of the nickel-plated cases.
The Numbers
| Spec | Value |
|---|---|
| Caliber | 357 Magnum |
| Bullet weight | 140 grains |
| Bullet type | Lehigh Xtreme Penetrator, fluted solid copper, lead-free |
| Muzzle velocity | 1550 fps (6-inch barrel) |
| Muzzle energy | 747 ft-lbs |
| Rounds per box | 20 |
| Case | Nickel-plated brass |
| Primer | Boxer, non-corrosive |
| Reloadable | Yes |
| Intended use | Self-defense, barrier penetration |
| Manufacturer | Underwood Ammunition (USA) |
You’ll find this load on our full 357 Magnum ammo roster, where we catalog barrier-blind defensive rounds and range-ready practice loads for wheelguns and lever carbines.
Safe Handling & Compliance
Federal law requires purchasers to be at least 18 years old for rifle and shotgun ammunition, and at least 21 for handgun ammunition. Ammunition cannot be shipped to certain states, counties, and cities — review our ammunition shipping restrictions before ordering. Store ammunition in a cool, dry location away from heat sources and out of reach of unauthorized users.
- Observe the four universal rules of firearms safety: treat every firearm as if it’s loaded, never point at anything you don’t intend to destroy, keep your finger off the trigger until ready to fire, and know your target and what lies beyond it.
- Check current state and local regulations before purchasing — some jurisdictions restrict lead-free projectile types or impose magazine-capacity limits that affect tubular-fed lever guns.
- This load generates higher chamber pressures than standard-velocity 357 Magnum — verify your revolver or carbine is rated for full-power magnum loads before firing.
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