Muzzle velocity alone certainly is no way to rate, relate, or compare cartridges' down-range performance. Here's a simple "quick and dirty" method of roughly comparing the down-range performance of two cartridges or two loads with different bullets in the same cartridge. This technique doesn't give you any details of retained velocity, retained energy, drop below aim, time of flight, or wind deflection. It sort of lumps all these specific performance details into one rough figure that's easy to compare with the parallel figure for another cartridge or load.<P>Multiply the muzzle velocity by the ballistic coefficient. <P>Hn = mv � bc <P>The higher result implies the "better" cartridge or load. Call it anything you like � Howell number (Hn), performance index (pi), relative performance index (rpi), whatever. It has no units, so it's just a number. <P>For a general comparison of two cartridges with different calibers and weights of bullets,<BR>� calculate the Hn of each typical load in each cartridge<BR>� calculate the average Hn of these loads in each cartridge<BR>and you'll have a single figure for each cartridge, making it easier to compare two or more cartridges succinctly.<P>For specific performance details for any cartridge, you'll have to go the long math route.
