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Modern Exterior Ballistics: Robert L. McCoy: 9780764338250: Amazon.com: Books

I believe the quote is "seek and ye shall find" grasshoppa

Krupp

In a ballistic program driving bands are mainly only relevant to artillery shells .

For small arms projectiles you enter the same size as the diameter of the bullet usually in calibres . So the bullet diameter might be .308 but the driving band diameter would be 1 .

To calculate calibres divide the value by the bullets calibre .308 -:- .308 = 1

If a bullets length is .75 of an inch then .75 -:- .308 = 2.435 calibres long.

Also some programs ask for a bullet turbulence code . L/T , L/L . This is lamina turbulent and lamina lamina. L/T is an air flow description of a spire point flat base and L/L is a spire point boat tail .

Then some have an Rt/R ratio input , most people will not have this value so if the bullet company says it's a Tangent ogive enter 1 . If they say it's a Secant ogive enter .6 .

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The spark photographs early in McCoy's book show un-finned projectiles as smooth sided. Some later ones in the book are of actual bullets, but those of experimental and standard shapes show smooth sides without driving bands. I am guessing that at some point after the war and perhaps as part of the numerous improvements they made at the BRL in succeeding decades, they may have gone to sabots to provide spin, but that's just a guess. They experimented with smaller rifled projectiles as part of the SARP program started in 1966 and did other things to see if smaller projectiles would fail to track the drag coefficients of larger ones due to their differing Reynolds numbers, the way spherical projectiles do, but didn't find significant issues.

McCoy always has his drawings in calibers so they can be scaled. These numbers are not always precise, however. In BRL-MR-3733 he has a sketch of the 173 grain M1 Type projectile with a 7 caliber ogive radius. Well, Hatcher shows it has a 2.1" nominal ogive radius, which is 7 times 0.300", and not 7 times 0.308". (You also find .300" used as the caliber in scaling targets for service rifle matches.) So, it's close, but not exact. That's OK for a couple of practical reasons: One is that forming dies don't turn out exactly consistent radii, so all bullets have some variation in this number even within a single lot number. From the drag table standpoint, dimensional differences as small as a radius difference of 2.100 vs 2.156 (7 times .308) make smaller differences in trajectory than are caused by velocity standard deviations and wind, so it's not really practically serious. Indeed, as Brian Litz points out, with experience you can guess a BC closely enough for general shooting purposes just by eyeballing the shape of a bullet and knowing its SD. Only at long ranges (800 yards and out) do higher precision numbers become important to keeping out of the transonic range and getting on paper.

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