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Message: <blockquote data-quote="338Shooter" data-source="post: 804782" data-attributes="member: 3449">It's all about impulse.  Impulse is defined as the integeral of the force vector from a time 1 to another time 2.  With a fast powder you get a spike of pressure which acts on the surface area of the back of the bullet (force) for a short time.  With a slower powder you get a smaller force for a longer amount of time.  If a fast powder and a slow powder are used to drive the same bullet to the same velocity the impulses will be equal in both cases, but the time windows will be different.  The slower powder will peak the pressure more near the muzzle, this high pressure gas can jet out after the bullet increasing felt recoil with Newton's third law similar to rocket engines.  If this is the case the same energy was delivered to the bullet, but there is more energy left in the form of the jet of gas causing more perceived recoil.  As you know, the slower powders are used in compensated guns to be able to harness this gas and limit muzzle flip.I believe the slower powders are used to achieve higher velocity because the peak pressure can be equal to the faster powders, but for a longer duration thus a higher impulse and a higher velocity.</blockquote>