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What is a subsonic load?

A subsonic load keeps the bullet below the speed of sound (roughly 1,125 fps at sea level), so no supersonic crack follows the shot. Most handloaders aim for 1,000–1,080 fps to keep a safety margin across changing temperature and altitude, because a load that measures 1,110 fps on a cold morning can go transonic on a hot afternoon and lose accuracy.

Popular subsonic cartridges

.300 Blackout with 190–220 gr bullets is the benchmark subsonic rifle cartridge, while 9mm Luger, .45 ACP and .45 Colt are naturally subsonic with standard bullet weights. .308 Winchester, 8.6 Blackout and .223 Remington can be loaded subsonic too, but they need heavy-for-caliber bullets and a fast twist barrel to stay stable at low velocity.

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Developing a subsonic load

Pick a heavy bullet and a fast-burning powder, then work up from a conservative start charge while watching case fill. Very low fill rates are the main risk in subsonic loading, so keep the charge dense enough to burn consistently, chronograph every step, and confirm the bullet still cycles the action and clears the suppressor bore.

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