Im looking to try some 9mm subsonic and all the load data is bases on the 147gn bullet. Why?
Full power 9mm loads with 147grain bullets are typically subsonic. You get a full power round to cycle the pistol action and it stays subsonic. A subsonic 9mm round based on 124 or 115 grain bullets would be less than full power (standard pressure) and might not have enough recoil to cycle the action. Also heavier bullets typically penetrate deeper than lighter bullets especially if launched at the same velocity.
It takes more energy to overcome the inertia of a heavier weight than a lighter weight. Heavier bullets require more energy input to travel the same velocity as lighter weight bullets. The speed of sound is purely a measurement of velocity. If your powder charge for two different bullets is 5 grains, and your firing a 115 gr bullet and a 147 gr bullet, the 147 gr bullet will have a dramatically lower velocity than the 115 gr bullet. Check out a secondary-school physics book, loc dog.
Thanks for the school lesson Doc.
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