Understanding Firearm Optic Mounting Systems

Before you buy any optic, light, or grip, you need to understand mounting systems. Using the wrong mount means your accessory won't fit — or worse, won't hold zero.

Picatinny (MIL-STD-1913)

The universal standard for top rails. Nearly all rifles and many pistols use Picatinny on top for optics. The slots are spaced at specific intervals for consistent mounting. If your gun has a "rail on top," it's almost certainly Picatinny.

M-LOK

Magpul's system for handguard accessories (lights, grips, rail sections). Rectangular slots that lock accessories with a twist. Now the dominant handguard attachment system, used by most modern AR-15 handguards. Recommended over KeyMod.

KeyMod

An older alternative to M-LOK with keyhole-shaped slots. Functionally similar but less popular now. The US military tested both and M-LOK won. If your handguard is KeyMod, adapters to M-LOK exist.

Dovetail

Common on older rifles, some pistol slides, and rimfire guns. Not standardized — widths vary (3/8", 11mm, 14mm). Dovetail-to-Picatinny adapters are available for most sizes.

Direct Mount / Proprietary

Some optics mount directly to specific slides or receivers (like Glock MOS plates or SIG Romeo Zero on P365). Always verify the exact footprint before buying.

How GunUpdate Helps

Our compatibility database knows which mounting system your specific firearm uses. Upload a photo or select your model — we'll only show accessories that actually fit, no guesswork needed.