Holosun HS403B

The HS403B mounts through a single Torx screw that pulls a cross bolt against the rail slot, and Holosun publishes a real number for it: 1.7 to 2.2 Nm, which is 15 to 19.5 inch-pounds. The included Torx wrench turns the screw but measures nothing, so a Torx bit in a torque driver is the only way to land inside that window.

Holosun supplies a high riser mount measuring 41.4 mm and a low mount measuring 19.3 mm. The 41.4 mm riser puts the dot at roughly the 1.63 inch height AR shooters call lower 1/3; the 19.3 mm mount sits the sight down near the bore for a rifle or shotgun with no need to clear irons. Unload the firearm and engage the safety before the optic goes near it.

The cell lives in a side tray held by two screws, so a battery change never breaks the mount and never costs you zero. One CR2032 ships taped to the second page of the manual itself, which is easy to throw out with the box.

The tray carries an o-ring. That seal is what backs the IP67 rating and the nitrogen fill, so look at it every time the tray is out. Runtime is up to 50,000 hours on one cell at brightness setting 6.

Elevation sits on top of the sight and windage on the right side, both slotted screws under protective caps. The cap doubles as the tool: seat the top of the cap in the slot and turn. Each click is 0.5 MOA, which the manual states as 13 mm at 100 meters, and total travel is plus or minus 1.4 m at 100 meters, or plus or minus 50 MOA.

Both axes run the opposite of rifle scope habit. Clockwise on the elevation screw lowers point of impact, and clockwise on the windage screw moves it left.

Two buttons on top of the sight run everything. A single press of "+" or "-" powers the sight on at the last setting used, and pressing both at once powers it off. There are 12 brightness settings, 10 for daylight and 2 for night vision devices, out of 13 positions counting off.

The factory sleep delay on the 403B is 8 hours of no movement, not the 10 minutes several other Holosun models use. That delay is programmable anywhere from 0 to 12 hours, and setting it to 0 disables the auto shutoff entirely.