Guys, Fire a SMK bullet .284" diameter, 175 grains weight at 2750 FPS muzzle velocity.
How do we figure out what it's velocity will be at various distances from the muzzle; like
at 300 meters, 600, 1000, etc.? Say we're at sea level in standard weather conditions.
Thanks very much.

What is the BC of the bullet? That is critical to the calculations.

quote:

Originally posted by Nakihunter:
What is the BC of the bullet? That is critical to the calculations.

Per company web site .533 faster than 2500fps.

http://www.sierrabullets.com/i...page=bc&bullettype=0

Ballistic Coefficients (SBT) Spitzer Boat Tail

.533 @ 2500 fps and above
.538 between 2500 and 2000 fps
.560 @ 2000 fps and below

This should help.........

Ballistic Calculators Link-Click Here

BigFive's Sierra "company" data illustrates the problem; BC changes with velocity, and it doesn't change in discrete steps, it changes the whole path as the speed changes.

At their best, trajectory and velocity calculations are just that, calculations. Calculations are no more than estimates of what actually happens.

There are better systems out there, but to date, only Berger uses it.

quote:

Originally posted by Jim C. <><:
BigFive's Sierra "company" data illustrates the problem; BC changes with velocity, and it doesn't change in discrete steps, it changes the whole path as the speed changes.

At their best, trajectory and velocity calculations are just that, calculations. Calculations are no more than estimates of what actually happens.

BC doesn't really change with velocity, IF your using the correct form factors BC. Where the problem comes up (and Sierra's data is proof) is when you use the velocity change rate (BC) for a roundnose bullet (G1) to determine the BC for a Spitzer Boat Tail (G7).

IOW you can't use the shape of a tractor trailer when looking at the wind drag of a F1 car

Of the Majors, Only Berger publishes the G7 data.

quote:

BC doesn't really change with velocity, IF your using the correct form factors BC. Where the problem comes up (and Sierra's data is proof)

Okay. I've looked at Sierra's data showing different BCs for different velocities and figgered they would know what they're talking about.

Also seems unlikely they would mix the results between a wad cutter (truck) and boat tail spitzer (race car) but maybe so. ??

Its been such a long time since I even looked at Math, but getting back to the original question, wouldn't determining the speed of a bullet at any distance during its flight in essence be determining the derivative (calculus) at that particular distance.

quote:

Originally posted by Jim C. <><:

quote:

BC doesn't really change with velocity, IF your using the correct form factors BC. Where the problem comes up (and Sierra's data is proof)

Okay. I've looked at Sierra's data showing different BCs for different velocities and figgered they would know what they're talking about.

Also seems unlikely they would mix the results between a wad cutter (truck) and boat tail spitzer (race car) but maybe so. ??

Jim
They use the truck numbers to make the car look better. IOW It makes the advertising more impressive.
The long range hunting guys pay a lot of attention to this very topic.
I hate to quote Wikipedia, but here's part of what they have on the topic
http://en.wikipedia.org/wiki/Ballistic_coefficient
Differing mathematical models and bullet ballistic coefficients
Most ballistic mathematical models and hence tables or software takes for granted that one specific drag function correctly describes the drag and hence the flight characteristics of a bullet related to its ballistics coefficient. Those models do not differentiate between wadcutter, flat-based, spitzer, boat-tail, very-low-drag, etc. bullet types or shapes. They assume one invariable drag function as indicated by the published BC. Several different drag curve models optimized for several standard projectile shapes are however available.
The resulting drag curve models for several standard projectile shapes or types are referred to as the:

G1 or Ingalls (by far the most popular)
G2 (Aberdeen J projectile)
G5 (short 7.5° boat-tail, 6.19 calibers long tangent ogive)
G6 (flatbase, 6 calibers long secant ogive)
G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets[10])
G8 (flatbase, 10 calibers long secant ogive)
GL (blunt lead nose)
Since these standard projectile shapes differ significantly the Gx BC will also differ significantly from the Gy BC for an identical bullet. To illustrate this a bullet manufacturer has published a G1 BC of 0.659 and a G7 BC of 0.337 for their 7 mm Match Target VLD bullet and has since published the G1 and G7 BCs for most of their target bullets.[11] In general the G1 model yields compariatively high BC values and is often used by the sporting ammunition industry.

Emphasis mine