| Ripp |
| (.577 member) |
| 26/08/17 03:55 AM |
Re: Behind-the-bullet- 6.5-284-Norma
|
Quote:
Any ballistic advantage the 6.5mm has over the .277 caliber is based solely on bullet availability. The Ballistic Coefficient (BC) of a bullet is it’s sectional density (SD) divided by its form factor. Compare a group of different caliber bullets that have the same shape and those with the highest sectional densities will have the highest BCs, i.e. the largest calibers. Using bullets of the same shape, any .277 caliber bullet would have a higher BC and a SD than its 6.5mm counterpart. It is the same with .257 caliber bullets compared to 6mm.
Consider the example of the Hornady 147 gr 6.5 ELD-match bullet given above. That bullet has an SD of 0.301. A 161.5 gr .277 gr bullet would achieve the same 0.301 SD and if made to the same shape as the 6.5 mm ELD bullet their BCs would be equal. On the other hand, it would be more comparable for Hornady to make something like a 168 gr .277" ELD and that would trump the BC of the 6.5.
But the market is what it is and bullet makers are not being called upon to make match bullets in diameters between 6mm and 6.5mm or between 6.5mm and 7mm.
Agree with your comments to a point..however in your example above, you are comparing a 147gr bullet with a 161.5 for a 270....my argument is when you compare the same weights the 6.5 clearly wins..furthermore when you increase the weight of the bullets the velocity in that calber also decreases..so now you are behind as soon as the trigger is pulled..if you have two bullets leaving the barrel, both having similar bc & sd, but on is traveling 200fps faster, the faster bullet will have the advantage 90% of the time..agree typically the heavier bullet carriers its energy longer, but.....
Ripp