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| Bullet R.P.M. How is bullet spin rate calculated? I asked around quite a lot and no one seems to know. Can you tell me? ************************ You can use the following formula to calculate the spin rate in revolutions per minute (r.p.m.) of a bullet as it emerges from the muzzle of a rifled barrel: RPM=720xMV/TW Where MV = muzzle velocity in feet per second (f.p.s.) TW=twist of rifling in inches per turn. For a .357 Mag. revolver having a twist of 8.75 inches per turn, firing a bullet at a muzzle velocity of 1235 f.p.s., the spin rate of the bullet in revolutions per minute is: RPM=720x1235/8.75=101,623. -William C. CAvis, Jr. ***************************** Reprint from american rifleman magazine, Sept 2001, pg 29. For more tech articles and many other interesting articles on safety, maintenance and firearm tests, JOIN THE NRA TODAY |