Last reviewed: 2026-04-18 by Jake Terry, FFL07/SOT3, NRA-certified firearms instructor.
The Underwood Xtreme Defender 10mm Auto ammo pairs a 115-grain Lehigh Xtreme Defense solid-copper projectile with Underwood’s full-power 10mm Auto loads, delivering 1700 feet per second and 738 foot-pounds of muzzle energy from a 5-inch test barrel. The fluted nose profile creates radial channels that force fluid inward under hydraulic pressure, building a permanent wound cavity over twice the diameter of traditional expanding hollowpoints — without relying on expansion that can fail after passing through wallboard, auto glass, or heavy clothing. Designed for self-defense applications where barrier-blind performance and deep, straight-line penetration are the priority, this load reaches up to 18 inches of penetration in ballistic gel, falling within FBI protocol guidelines.
Performance at a Glance
Underwood machines each 115-grain Xtreme Defense projectile from solid copper, eliminating lead while maintaining sectional density of 0.103 and a sharp cutting profile that defeats intermediate barriers. The nickel-plated brass cases resist tarnish, enhance feeding in all action types, and remain reloadable after firing. Flash-suppressed powder preserves low-light vision if you fire in dim conditions. Boxer primers are non-corrosive. Each 20-round box ships ground (DOT-regulated) and arrives ready for duty carry, home defense, or backcountry sidearm applications where you expect to punch through bone, brush, or structural barriers before reaching vitals.
The Numbers
| Spec | Value |
|---|---|
| Caliber | 10mm Auto |
| Bullet weight | 115 grains |
| Bullet type | Lehigh Xtreme Defense (fluted solid copper) |
| Muzzle velocity | 1700 fps |
| Muzzle energy | 738 ft-lbs |
| Test barrel length | 5 inches |
| Rounds per box | 20 |
| Case | Nickel-plated brass |
| Primer | Boxer, non-corrosive |
| Reloadable | Yes |
| Lead-free | Yes |
| Intended use | Self-defense |
| Manufacturer | Underwood Ammo |
You’re looking at full-power 10mm Auto velocities in a package engineered to defeat barriers that stop conventional hollowpoints. For additional Underwood 10mm Auto loads — from hardcast hunting rounds to lighter-recoiling practice ammo — browse our complete Underwood 10mm Ammo selection.
Safe Handling & Compliance
Federal law requires purchasers to be at least 21 years old 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 gun as loaded, never point at anything you’re not willing to destroy, keep your finger off the trigger until ready to fire, and know your target and what lies beyond it.
- Verify that 10mm Auto chambering matches your firearm’s headstamp before loading. Consult your firearm’s manual for maximum pressure limits and barrel length recommendations.
- This load produces full-power 10mm Auto recoil and report. Wear eye and ear protection. Verify suppressor host rating before use with suppressor-equipped firearms.
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