Last reviewed: 2026-04-18 by Jake Terry, FFL07/SOT3, NRA-certified firearms instructor.
Underwood 10mm Auto 140 grain ammunition loaded with the Lehigh Xtreme Penetrator represents a shift from traditional expanding bullets to a monolithic, barrier-blind projectile. The 10mm Auto cartridge, developed in the 1980s for FBI service use, delivers magnum-level energy in a semi-automatic platform. Underwood pairs this high-pressure chambering with Lehigh Defense’s CNC-machined solid copper bullet — a fluted design that creates hydraulic pressure spikes in tissue and maintains structural integrity through glass, drywall, and heavy clothing. This 140 grain load exits a 5-inch test barrel at 1500 feet per second, generating 700 foot-pounds of muzzle energy. The projectile’s blunt nose and fluted channels drive fluid radially outward, producing a permanent wound cavity without traditional expansion. For shooters requiring barrier performance and consistent penetration depth in a lead-free package, this load offers a geometry-based wounding mechanism that does not rely on bullet deformation.
Built for the Box
Underwood manufactures this load in their Arkansas facility, using flash-suppressed powder that preserves low-light vision. The Lehigh Xtreme Penetrator bullet is precision-turned from solid copper bar stock — the fluted nose channels fluid away from the projectile’s path, increasing hydraulic velocity and creating temporary stretch cavities that collapse into a permanent wound channel. Underwood states the projectile achieves over twice the penetration depth of conventional hollow-point bullets while maintaining straight-line tracking through intermediate barriers. Nickel-plated brass cases provide enhanced feeding in all action types, resist tarnish during storage, and clean more easily during the reloading process. Boxer primers are non-corrosive, and cases remain reloadable after firing. The blunt ogive feeds from all 10mm magazines tested — single-stack 1911s, double-stack Glocks, and extended competition magazines cycle the round without hang-ups.
Specs at a Glance
| Spec | Value |
|---|---|
| Caliber | 10mm Auto |
| Bullet weight | 140 grains |
| Bullet type | Lehigh Xtreme Penetrator (solid copper, fluted) |
| Muzzle velocity | 1500 fps (5-inch barrel) |
| Muzzle energy | 700 ft-lbs |
| Rounds per box | 20 |
| Case | Nickel-plated brass |
| Primer | Boxer, non-corrosive |
| Lead-free | Yes |
| Reloadable | Yes |
| Intended use | Self-defense |
| Manufacturer | Underwood Ammo |
This load ships from Underwood as DOT-regulated hazmat. The 140 grain bullet sits at the lighter end of the 10mm spectrum — most defense loads range from 135 to 200 grains. The lighter projectile achieves higher velocity while maintaining magazine capacity and reducing felt recoil compared to 180-grain or 200-grain options. For shooters running Underwood 10mm ammo in Glock 20, Glock 29, Springfield XDM, Sig P220, or 1911 platforms, this bullet weight balances flat trajectory, reduced muzzle flip, and barrier performance. The solid copper construction eliminates lead exposure at indoor ranges and complies with lead-free hunting regulations in California and other restricted areas.
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.
- Treat every firearm as if it is loaded; keep the muzzle pointed in a safe direction at all times; keep your finger off the trigger until ready to fire; be sure of your target and what lies beyond it. Review the NRA’s Four Rules of Gun Safety for complete handling protocols.
- Verify current federal, state, and local laws governing ammunition purchase, possession, and use in your jurisdiction. Some municipalities restrict hollow-point or barrier-penetrating projectiles for civilian carry.
- This product contains materials known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, visit www.P65Warnings.ca.gov. Lead-free copper projectiles reduce range exposure but still require proper ventilation during firing.
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