Underwood 357 Sig Ammo 115 Grain Lehigh Xtreme Penetrator Fluted Lead Free Box of 20

Last reviewed: 2026-04-18 by Jake Terry, FFL07/SOT3, NRA-certified firearms instructor.

The Underwood 357 Sig 115 grain Lehigh Xtreme Penetrator is a lead-free defensive load engineered for straight-line penetration through intermediate barriers — glass, wallboard, heavy fabric, bone — without the expansion failures common to jacketed hollow points. Progressive nose geometry and radial flutes channel hydraulic pressure outward, creating a permanent wound cavity diameter that exceeds most expanding bullets while maintaining structural integrity through hard contact. At 1450 fps from a 4-inch barrel, this load delivers 537 ft-lbs of energy and a flat trajectory inside 50 yards, making it a top-tier choice for duty carry and vehicle defense where barriers are likely. The 357 Sig cartridge is a bottlenecked semi-auto round that duplicates 125-grain 357 Magnum ballistics from a semi-automatic platform, developed in 1994 by SIG Sauer and Federal for law enforcement agencies seeking more authority than 9mm in a service pistol package.

Built for the Box

Each projectile is CNC-machined from solid copper bar stock — not pressed powder metal, not sintered frangible. The nose features six radial flutes that compress tissue and fluid inward as the bullet advances, then redirect that energy outward in high-pressure spikes, tearing a larger permanent channel than a flat nose or ball round would cut at the same diameter. Underwood states the fluted design produces a wound cavity two to four times greater than conventional FMJ, independent of expansion. The solid copper construction resists deformation when striking auto glass, plywood, drywall, and bone — barriers that frequently plug or collapse hollow-point cavities and reduce penetration depth. Underwood loads these rounds in nickel-plated brass cases treated with the Ducta-Bright 7a process, which maintains case ductility for multiple reloads without the embrittlement associated with older nickel plating methods. Boxer primers, non-corrosive propellant, suppressor-safe pressure curve. This is barrier-blind ammo: it penetrates predictably regardless of what it hits first.

The Numbers

The 115-grain weight is lighter than the 124- and 147-grain loadings common in 9mm, but the 357 Sig case delivers higher velocity and flatter trajectory at defensive distances. The Xtreme Penetrator’s fluted geometry is optimized for straight-line wound channel creation rather than expansion, making it effective in gelatin or tissue whether or not a hollow point would have opened. Underwood field-tests every lot with real firearms — SIG P229, Glock 31/32/33, Springfield XD-M — to verify function and point-of-impact. If you carry a 357 Sig pistol and your threat model includes vehicle glass, interior walls, or attackers behind cover, this load provides consistent terminal performance without the variable expansion behavior of bonded or conventional JHP designs. Find more barrier-blind and defensive loads in our 357 Sig ammo category.

Who It’s For

Law enforcement officers who need reliable penetration through car doors and windshields. Armed professionals working in vehicle or structure environments where intermediate barriers are probable. Carriers in states or jurisdictions that restrict lead projectiles. Shooters who want predictable terminal ballistics independent of hollow-point expansion. If you run a duty-sized 357 Sig pistol (P229, Glock 31, M&P 357) and prioritize straight-line penetration over temporary cavity expansion, the Xtreme Penetrator is purpose-built for that mission. The solid copper construction also makes this load compliant with lead-free range requirements and California hunting regulations, though its intended role is human defense, not game. Reloadable nickel cases mean you recover brass value if you hand-load, and the non-deforming projectile ensures you’re not chasing jacket fragments or lead smear in suppressor baffles.