Classic interior ballistics literature has long pointed out that at any given peak pressure (60,000 lb/sq in. in each barrel, for example), a .224 barrel erodes faster than a 6mm barrel, which in turn erodes faster than a .308 barrel, under the same situation and circumstances � rate of fire, cooling intervals between firings, and such.<P>It's even long-known that the difference lay in a discrete mathematical ratio � expressed in two ways:<BR>� the ratio of the circumference of the bore's cross-section to the area of its cross-section<BR>� the ratio of the surface of the bore to the volume of the bore, with a given length of rifled bore<P>"These ratios" are the same ratio expressed two ways.<P>Now with Mathcad's help, I've just run, in a few minutes, what would've taken me hours and hours to do with a calculator (and days to get for-sure RIGHT).<P>I ran the equations through Mathcad, for a .224 barrel and a 6mm barrel, both with 24 inches of rifled bore. I knew already that the .224 would erode faster but didn't know exactly HOW MUCH faster. Now I know.<P>The surface of 24 inches of a .224 barrel is 16.889 sq in. Its volume is 0.946 cu in., for a surface-to-volume ratio of 17.853-to-1.<P>The surface of 24 inches of a .244 barrel is 18.397 sq in. Its volume is 1.122 cu in., for a surface-to-volume ratio of 16.397-to-1.<P>The .224's ratio is 8.9% greater than the 6mm's, which means that the .224 erodes 8.9% faster than the 6mm at the same peak pressure, with all other conditions the same.<P>Now you know too. (Oh, that's OK � no charge! �o)<P>Mathcad has really opened up and shone light into a passel of dark corners here! Ain't it fun, learning something new 'n' useful? <P>
