Why does it seem so much easier to get a larger caliber to have a high BC than a small caliber? Some may blame the desire to go superfast and thus use light, low BC bullets, but that doesn't entirely make sense. For a high BC .17 or .22 bullet you have to go with a fast twist barrel, while a .308 or .338 can get by with a much slower twist for a bullet with a similar BC. What factor is at play here?Thanks.
Heavier bullets are available in the larger calibers. To get a truly high BC in a small caliber, it would need to be unrealistically long. The heavier weights "carry" better downrange. Throw a ping pong ball and a golf ball. Both roughly the same size, but the heavier golf ball carries much better.
You just can't put enough weight in the smaller calibers & keep them stabilized. Stabilization is dependent on the twist being appropriate to the bullet length, not necessarily weight.
I believe it's because the bullet is actually pushing air out of the way, therefore a heavier bullet has more energy to disapate as it does that. Not very technical but I believe it's true.
quote:Originally posted by Geo: Why does it seem so much easier to get a larger caliber to have a high BC than a small caliber?
Pure math. As a bullet grows in diameter; with like proportions; the frontal area increases by the square while the weight increases by the cube. The higher weight/frontal area ratio gives it more ability to withstand slowing down.
Think of it this way. A mouse has much more surface area in proportion to it's mass than an elephant has surface area in proportion to it's mass. Just a law of physics concerning surface area to mass(same type material anyway) UNLESS the elephant is hollow, flesh compared to flesh. Therefore, the mouse has much more wind resistance(drag) proportionally speaking than does the elephant. An elephant will fall faster and harder than a mouse when thrown off a building. Same for as bullet bores increase. Also, the larger the diameter of the bullet, the less elongation of the bullet you get proportionally speaking as proportional weight goes up. Thus, the big bores require less twist to stabalize those high BC bullets. The .243, 25s, and .270 were originally designed for only moderately long bullets so work fine with the 1 in 10 twist. But the 6.5x55, 7x57 and .30-06 were originally designed to handle very long bullets of 160, 175 and 220 grains thus requiring a 1 in 8, a 1 in 9 and a 1 in 10 twist to work. Notice how the necessary twist rate to stabalize the very long bullets slows down as the bore diameter increases. A .458 only requires a 1 in 14 or 1 in 16 twist for the high BC bullets. Well, you get the gist of it.
It isn't the weight of the bullet that requires faster twist to stabilize it, it is the length. Bullets with a smaller diameter are much lighter for the same length than heavier bullets. It is the law of cubes. Bullets of the same length require the same twist to stabilize them. Naturally those with greater diameter are much heavier. Just like boats, a 16 foot boat has more than twice the displacement as an 8 foot boat.
The lighter the bullet is in a given cartridge the shorter it is. heavy bullets grow in length and the higher it's SD+BC is. Short fat bullets fly through the air very poorly and have very low SD+BC. Long sleek heavy bullets fly through the air very well and have high SD+BC. The advantage of long sleek bullets is exceptional long range performance. Short fat bullets are better suited to distances under 200 yards. Hollow Point Bullets are longer than a soft point bullet of the same weight. Hollow Point Boat Tail bullets are longer than Hollow Point or Soft Point flat base bullets of the same weight. Choosing the right bullet for the right job is very important no matter what your shooting game is.
