The 75 grain Sierra HP flat base is a much shorter bullet than a similar weight BTHP bullet, or a 100+ grain SP or HP bullet. In a given 243 Win twist rate (like a 1:10″ barrel twist) and slow subsonic speeds, a shorter, flat base bullet is more stable than a longer BTHP match bullet is. Bullet length is a major factor in how stable a bullet is in a certain twist rate. 243″ bullet to fully stabilize at subsonic speeds in a given twist rate, bullet stability becomes a huge factor for it to stabilize and shoot well. Why use a 75 grain HP bullet? Most 243 Win barrels will have a 1:10″ twist barrel, with some having a 1:9″ twist or faster. This is with new high-end Norma brass and Sierra 75 grain HP bullet. 223 caliber bolt-action rifle firing low-velocity (subsonic) ammunition using a GEMTECH G5-5.56 suppressor.Ĭompared to the high-velocity (supersonic) unsuppressed condition, the combination of subsonic low-velocity ammunition and a firearm suppressor provided a reductions of 45, 38, 40, and 48 dB, peak sound pressure level at the muzzle, left, right ears and behind the shooter, respectively.New!! By request, I recently developed a 243 Winchester SUBSONIC round shooting the 75 grain Sierra HP at 1030 fps in 22″ barrel. The peak sound pressure levels of a Remington 700. 223 caliber bolt-action rifle firing high-velocity (supersonic) ammunition using a GEMTECH G5-5.56 suppressor. Specific reductions depend on the ammunition and suppressor. Main article: Suppressor § Subsonic ammunition and reduced sonic signatureĬombined with firearm sound suppressors, subsonic ammunition may significantly reduce sound levels compared to normal ammunition. These are designed from the start as dedicated subsonic projectile systems. 45 ACP ammunition load, of a 230 grain bullet at 850 feet per second, is naturally subsonic.Īlternatively, specialized firearms and ammunition may be used to optimize total subsonic ammunition effectiveness. For example, the traditional American military standard. Some ammunition types were inherently designed with heavier, slower standard bullet weights and velocities. Subsonic ammunition with normal bullet weights often fails to properly function in such firearms. Subsonic loads for 9mm commonly use 9.5 grams (147 gr) bullets at velocities of 300 metres per second (980 ft/s).įor these ammunition loads, balancing bullet weight and velocity are required to ensure that the ammunition will still reliably cycle semi-automatic firearms. In this instance, heavier bullets are loaded in standard ammunition, which reduces muzzle velocity below the speed of sound.Īs an example, the very common 9×19mm Parabellum standard military round is a 7.5 grams (116 gr) bullet at velocities typically around 360 metres per second (1,200 ft/s). Standard calibers Subsonic versions of standard rounds 1.1 Subsonic versions of standard rounds.
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