The U designation stands for Ultra, which identifies the high-output variant of the X300 series. The X300 Ultra produces 1,000 lumens, significantly more than earlier generations of the X300 platform. The Ultra series also incorporates the refined TIR lens design and the improved ergonomic switch geometry that is wider and shorter for more positive activation under stress. The B suffix in X300U-B identifies the Thumbscrew mounting variant as opposed to the T-slot rail key variant (X300U-A); output, optics, and body are identical between the two.

A TIR (Total Internal Reflection) lens is a single-element optical component that surrounds the LED and captures emitted light at all angles, redirecting it forward through internal reflection rather than relying on a parabolic reflector behind the LED. In a reflector design, a significant portion of the light emitted sideways must bounce off a reflective surface before exiting the lens — introducing scatter and optical inefficiency. The TIR lens captures that side-emitted light directly, producing a more controlled beam with a sharper hotspot, more consistent spill, and less wasted output. For target identification at tactical distances, the result is a beam that reads clearly at the center without the dark annular rings common in lower-quality reflector lights.

The X300U-B uses a thumb-operated clamping screw to secure the light body to the Picatinny rail. The light slides onto the rail from the front and the thumbscrew is tightened by hand until the clamp bites into the rail cross-slots. No tools are required for mounting or removal. SureFire’s rail clamp design is engineered to remain secure under the sustained recoil of pistol and carbine fire. The light does not require a separate locking mechanism; the clamp engagement with the cross-slots provides positive retention. For users who transfer the light between multiple firearms, removal takes a few thumb-turns and the light detaches cleanly.

The DG Switch is an optional replacement grip panel designed for specific handgun models that replaces the trigger guard area panel and incorporates a pressure pad, allowing the shooter to activate the X300 Ultra by squeezing the grip rather than reaching for the tail switch. This allows faster, more natural light activation during a draw stroke and keeps the trigger finger out of the guard until needed. The XT Switch is a remote pressure pad with a tape-mount cable designed for long guns (carbines, shotguns), allowing the shooter to activate the light from a forward handguard position without breaking grip. Both are sold separately and are compatible with the X300 Ultra platform. Consult SureFire’s compatibility chart for DG and XT switch fitment by specific firearm model.

No. The X300U-B operates in two modes: constant-on (1,000 lumens) and momentary-on (1,000 lumens). There is no strobe, reduced-output, or secondary lighting mode listed for this model. The X300 Ultra is designed as a single-output professional tool — 1,000 lumens on demand, with the choice of momentary or constant-on activation. Users who require a strobe mode should compare this model to alternatives. For duty, competitive, and home defense use, the constant and momentary modes cover the full range of operational scenarios the X300U-B is designed for.

MIL-SPEC hardcoat anodize (MIL-A-8625 Type III) is an electrochemical surface treatment that converts the outer layer of aluminum into aluminum oxide — a ceramic-hard surface significantly more abrasion-resistant than bare aluminum or standard Type II anodize. On weapon lights, this translates to resistance against holster wear, impact scoring, and corrosion from sweat, moisture, and field chemicals. The X300 Ultra’s housing is built to maintain its structural and cosmetic integrity through sustained professional use. MIL-SPEC hardcoat is the standard specified for firearm components, tactical lights, and equipment intended for law enforcement and military service.