BC is calculated with more than just the bullet weight.
It's a function of the aerodynamic drag, or lack thereof. A streamlined bullet of a given weight and diameter will always have a better BC than a less-streamlined bullet of the same weight and diameter. SD is calculated quite simply as the ratio of the bullet's diameter to weight, there are no provisions for factoring in whether a bullet is nose heavy, tail heavy, or balanced. Those balance characteristics of a bullet influence stability and yaw, both enroute to the target and inside the target, but don't do a darned thing to SD and by default BC. The SD will remain the same because those bullets have the same diameter and weight, but the BC is better due to the cleaned-up aerodynamics. And that rubbery tip is still a hell of a lot more aerodynamic than the traditional flat nose of factory .30-30 rounds. Don't believe me? Take the rubber point off and see what the BC does. It'll nosedive, because you're back to a flat nose in the wind again.
For example, a Hornady 100 grain round nose 6mm bullet has a BC of .216; a Hornady 100 grain spire point 6mm bullet has a BC of .357, and a Hornady 100 grain boat tail spire point 6mm bullet has a BC of .400. All three of these bullets have a sectional density (which is the ratio of a bullet's diameter to its weight) of .242, because they are all .243" in diameter and weigh 100 grains. But the more streamlined bullets have a higher ballistic coefficient. BS? I doubt it.
I've worked with several 6.5mm bullets that have downright gorgeous BC numbers, particularly those in the 120 through 142gr weights. What's interesting is the variety of different BC numbers one can get from just modifying the ogive and boattail on bullets of otherwise similar weights.
Myself, I'm a great fan of pointy bullet .45-70 loads and their higher BC numbers, btw. 800-1000 yard silhouette and Quigley match shooters are, too, and rightfully so.
Those of you out there in THR land who have a Savage 340, Remington 788, or Winchester Model 54 are well aware of how good a combination of spitzer bullets and the .30-30 Winchester cartridge is.