The meplat (from the French word "méplat" meaning "flat surface of a cylinder") is the technical term for the flat or open tip on the nose of a bullet. The shape of the meplat is important in determining how the bullet moves through the air. In particular the size and shape of the meplat has a significant effect on the ballistic coefficient of a bullet.[1]
Theory
Trimming the meplat (cutting the tip of the bullet, thus increasing its area[2]) decreases the bullet's ballistic coefficient, increasing drag, and making it more susceptible to wind drift. So even though the grouping will be tighter, the time of flight and wind drift will be slightly greater.[3]
Pointing the meplat (reducing its area) involves pressing the bullets into a special die. This decreases the size of the meplat which increases the ballistic coefficient, which reduces drag, time of flight, and wind drift of the bullet.[3][4] Some target shooters sort their bullets by weight, point their bullets, and then trim them to the same meplat width to ensure the greatest possible consistency.[3]
The shape of the nose of an axisymmetric projectile that gives it the least possible aerodynamic drag at hypersonic speeds always has a meplat, the diameter of which depends on the length of the nose.[6]
Varying meplats
If the meplats on a group of bullets are uneven, the trajectory of the bullets will vary which will cause the bullets to strike the target at different vertical locations.[3] Bullets of the same mass that have similar-shaped meplats will travel through the air in nearly identical fashion, making it easier to group shots together or hit a target multiple times. For this reason, competitive shooters and snipers often trim or point their meplats to uniform shape.[3]
^A.J. Eggers, Jr., Meyer M. Resnikoff, and David H. Dennis, "Bodies of Revolution Having Minimum Drag at High Supersonic Speeds", NACA Report 1306, 1955.
