Was playing around with the ballistics calculator on Hornady's site and was wondering , does anyone know , or know where to look to find the B.C. and assorted specifics of a 655 gr. 50 Cal bullet (pulled bullets for a BMG) ?
Ballistics
- Thread starter Ice-Pick
- Start date
- Location
- Somewhere on the Hudson Bay Coast
Well, Barnes lists 3 .50 BMG bullets in their manual; in 600, 750, and 800 grs. The 600 gr X bullet has a BC of .702, and is probably the closest in shape to the 655. As a guess I'd say the 655 gr bullet has a BC of about .766.
Ball
Actually, yeah, i wasn't thinking, its Pulled M33 Ball bullets.
most of it is anyways, only worried about the 655 gr. stuff.
wanna know what to expect when i move back, don't wanna waste 750's till sure of the results.
thanks guys
Actually, yeah, i wasn't thinking, its Pulled M33 Ball bullets.
most of it is anyways, only worried about the 655 gr. stuff.
wanna know what to expect when i move back, don't wanna waste 750's till sure of the results.
thanks guys
- Location
- Somewhere on the Hudson Bay Coast
oppy said:
I think the skies the limit. The basic calculation is Sectional Density (Bullet weight in pounds X the square of the caliber) X a form factor, which varies with the aerodynamic design of the bullet. If we consider that the SD of a 14" naval gun with a projectile that is 6' long and weighing 1760 pounds, is 8.98, this in turn is multiplied by a form factor, I have no idea of what it would be, but lets say it's 5.143. The calculation results in a BC of 46.184. This explains how a bullet with a MV of 3000 fps can have a range of nearly 20 miles.
All the BC is is a co-efficient of a theoretical bullet with a BC of '1'. So if your bullet is half as efficient as this fictional bullet, it's .5. If it's twice as efficient, then it's 2.0.
It's a VERY imperfect calculation. There are a few 'drag functions' or 'shapes' of these theoretical bullets, most commonly used is the 'G1' function. The function accounts for things like velocity, weight, length, shape, and a few other things. Problem is, this function doesn't perfectly describe all bullets out there, yet is universally applied. The same drag function is applied to RN's, flat bases and boat tails indiscriminately. It just doesn't fit properly.This is why some manufacturers provide a few different BC's to describe their bullets at different speeds. This is a big, ugly kludge, a proper drag function takes speed into account as a variable in the function.
The functions themselves break down around the 1300 fps 'trans sonic' mark (exact vel. depends on the bullet length). Even if you've got the right drag function for your bullet shape, the rules of fluid dynamics are vastly different at sub- and super-sonic velocities, and then there's the 1100-1300-ish fps 'trans' sonic transition zone which is even messier, and in truth, no one really understands it.
Nevertheless, BC's are usually 'accurate enough' to provide usable data in most cases.
It's a VERY imperfect calculation. There are a few 'drag functions' or 'shapes' of these theoretical bullets, most commonly used is the 'G1' function. The function accounts for things like velocity, weight, length, shape, and a few other things. Problem is, this function doesn't perfectly describe all bullets out there, yet is universally applied. The same drag function is applied to RN's, flat bases and boat tails indiscriminately. It just doesn't fit properly.This is why some manufacturers provide a few different BC's to describe their bullets at different speeds. This is a big, ugly kludge, a proper drag function takes speed into account as a variable in the function.
The functions themselves break down around the 1300 fps 'trans sonic' mark (exact vel. depends on the bullet length). Even if you've got the right drag function for your bullet shape, the rules of fluid dynamics are vastly different at sub- and super-sonic velocities, and then there's the 1100-1300-ish fps 'trans' sonic transition zone which is even messier, and in truth, no one really understands it.
Nevertheless, BC's are usually 'accurate enough' to provide usable data in most cases.
- Location
- Somewhere on the Hudson Bay Coast
Prosper's post is excellent. In the end, if you intend to shoot at long range, you will find that neither the trajectory nor the retained velocity, from tables or software, is absolutely accurate. The best way is to develop a range card for your own rifle, ammo, and location, which you can refer to for long range come-ups.
If you want to be able to figure out a realistic BC for your own application, Google "Load From a Disk".
If you want to be able to figure out a realistic BC for your own application, Google "Load From a Disk".
