.308 Win. (7.62 x 51) Subsonic

The .308 Winchester (7.62×51mm NATO) is a versatile and widely used rifle cartridge that, while originally designed for supersonic performance, can be successfully adapted for subsonic applications with proper load development. As a larger case with significant internal volume, one of the primary challenges when loading the .308 Win subsonically is managing the powder charge to avoid erratic ignition and pressure spikes — often referred to as "detonation" or "secondary explosion effect" — caused by underfilled cases.

To load the .308 Winchester for subsonic performance, shooters typically use heavy bullets in the 180–220 grain range, with 200gr or 220gr bullets like the Sierra MatchKing, Hornady A-MAX, or Lapua Subsonic FMJ being popular choices. The goal is to keep muzzle velocities around 1,000–1,050 fps, depending on atmospheric conditions, to remain below the speed of sound while maintaining consistent ballistic performance.

Fast-burning powders that are well suited for small-volume charges — such as Trail Boss, Hodgdon H4895 (with reduced load data), Vihtavuori N32C (Tin Star), or IMR 4227 — are typically recommended. Using fillers or case positioners is another method reloaders may employ to ensure consistent powder ignition, though extreme caution and testing is required.

Barrel twist rates of 1:10 or faster are preferred to ensure stable flight of longer, heavier subsonic bullets. When suppressed, the .308 Win can be very quiet with subsonic loads, making it a viable option for tactical applications, target shooting, and some hunting situations. However, energy levels are reduced significantly, so proper shot placement and bullet selection are critical for ethical results.

While not as inherently efficient as purpose-built subsonic calibers like the .300 Blackout, the .308 Win remains a strong choice for subsonic use in platforms where caliber flexibility and suppressor use are desired.