Long range shooting query

It uses their several BC's instead of one as Litz' all others do. That, to me, means that 90-gr bullet's BC drop to 60% of what it started out with in 1000 yards of flight cannot have the same trajectory as one with a constant BC.
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Because of this . I've never used the highest BC for a given bullet . I always input the mid range BC into the calc in order to get what I think would be a more realistic calculation

80gr smk
.420 @ 2200 fps and above
.400 between 2200 and 1800 fps
.393 @ 1800 fps and below
I input a BC of .400 because the bullet will travel at all of those velocities out to 1k .

The 90gr smk with a BC of .480 i get pretty much the same numbers as Jimro except my calc saws the bullet never goes subsonic . At 1k it's velocity is still 1237fps 900yds 1334fps

When you get the program please come back and post your results
 
Bart B.,

Litz's data uses the G7 reference model, which equivalently maps the multiple BC's of the G1 model that Sierra advertises. The JBM software that has (Litz) next to the projectile is the data that Litz gathered testing the bullet in real conditions.

Either method of predicting ballistic performance will work just fine.

Jimro
 
Metal God,

The 90gr smk with a BC of .480 i get pretty much the same numbers as Jimro except my calc saws the bullet never goes subsonic . At 1k it's velocity is still 1237fps 900yds 1334fps
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The calculation doesn't show subsonic until after 1k, but the "transonic region" is about Mach 0.8 to 1.2. The 90 SMK hits Mach 1.2 at 900 yards in that ballistic solution, so you can't always expect stable performance through that velocity.

For example, ever wonder how a subsonic 168gr SMK load from a 300 Blackout can have a very stable BC across the usable range of the load? By starting out subsonic the bullet drops down into a stable BC and stays there. Google "wave drag transonic" and click on the images to see the increasing drag on a solid body in the transonic region, which is why Sierra shows higher BC's for higher velocities.

Ballistics is fun stuff :P

Jimro
 
As Sierra established their G1 numbers from time of flight tests with many velocities, I don't see how a fixed G7 number will yield the same results as multiple G1 numbers.

Gotta get Sierra's Infinity software then compare it with Berger and JBM software for the same bullet.
 
There is more difference between G1 and G7 than just a different number to start out with. The calculations to use them are different. In earlier times, there were huge tables to look up drag functions. I don't know if the computer programs now use digital lookup tables or if they use approximating equations. Maybe Mr Litz says which in his book, I can't find it in his articles.

See the article at
http://www.bergerbullets.com/a-better-ballistic-coefficient/

The key point is
It’s a relatively well known fact that the BC of a bullet is different at different velocities. Not many shooters know why it changes, or what the consequences are. To understand why a BC changes at different speeds, we have to go back to the definition of BC, which is: The ability of the bullet to maintain velocity, in comparison to a ‘standard projectile’. It’s the ‘standard projectile’ part of the definition that we need to key in on. What is the ‘standard projectile’? What does it look like?

To date, the ‘standard projectile’ used to define BCs for the entire sporting arms industry is the G1 standard projectile. The G1 standard projectile which is shown in Figure 1 has a short nose, flat base, and bears more resemblance to a pistol bullet or an old unjacketed lead black powder cartridge rifle bullet than to a modern long range rifle bullet.



The reason why the BC of a modern long range bullet changes so much at different velocities is because modern bullets are so different in shape compared to the G1 standard that its BC is based on. In other words, the drag of a modern long range bullet changes differently than the G1 standard projectile, so the coefficient relating the two (the ballistic coefficient) has to change with velocity.

There are several ways to manage the problems caused by the dependence of BC on velocity. One way is to use a G1 BC that’s averaged for the speed range you’re interested in. This will get you close, but what if the BC of the bullet is advertised for a speed range that’s different than what you’re interested in? It’s not easy to adjust the BC for different average velocities. Another way to deal with the problem of a velocity dependant BC is to give the BC in several velocity ‘bands’ (Sierra bullets uses this approach to advertise the BCs of their bullets). This can be an accurate approach, but it leaves a lot of room for misinterpretation. For example, many shooters don’t understand why there are different BCs and choose the wrong one. Furthermore, not all ballistics programs allow you to input multiple BCs. In short; the use of the non-representative G1 standard (Figure 1) to define BC is responsible for the velocity dependence and associated problems with BCs.

A better standard for long range bullets
If you look at the G1 standard projectile again in Figure 1, you might think; “it’s too bad there isn’t a standard that’s more representative for modern long range bullets”. In fact, there are several standard projectiles, all with different shapes, that are much more representative of modern long range bullets than the G1 standard. The standard that bears the closest resemblance to most modern long range bullets is the G7 standard, shown in Figure 2.

As you can see, the G7 standard projectile, with its long boat tail and pointed ogive bears a much stronger resemblance to a modern long range bullet than the G1 standard projectile. As a result, the BC of a modern long range bullet that’s referenced to the G7 standard is constant for all velocities! In other words, a trajectory that’s calculated with a ‘G7 BC’ doesn’t suffer from the same velocity dependence problems and inaccuracies as calculations that are made with a G1 BC.


Sierra gives a lot of history and the basis for their use of G1 BC by velocity brackets
http://www.exteriorballistics.com/ebexplained/articles/the_ballistic_coefficient.pdf

The ballistic coefficient of a bullet is a scale factor (a number) which divides the standard drag to predict the actual drag on the real bullet.

A standard drag function (G1, G7, etc.) is a table of numbers. Each pair of numbers in that table are (1) a specific speed of the bullet in the air, and (2) the drag deceleration of the standard bullet at that bullet speed, divided by that bullet speed.

Ballistic coefficients are relatively easy to measure in a shooting laboratory. The technique is to measure initial velocity and final velocity of each fired round (using chronographs) over a measured range distance between the chronographs. Then a software analysis program is used to compute the ballistic coefficient value which would cause the standard bullet starting at the initial velocity to have a computed final velocity equal to the measured final velocity.

Because a ballistic coefficient always relates to a specific standard drag model, say G1, that ballistic coefficient cannot be used with any other drag model, say G7.
 
If the .223 Rem is such a great tack (or pin) driver for distant targets, why ain't it popular with long range group and score match winners shooting bolt action rifles?

Could it be they're still in the dark about what's best and have problems finding their ammo when it's too tiny and can't be easily found in low light situations?
 
Could it be they're still in the dark about what's best and have problems finding their ammo when it's too tiny and can't be easily found in low light situations?
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Yeah- Yeah! That must be it!

I'm going to pull a very nice Rem 700 in .223 out of it's mothballs in the gun cabinet now for the next range trip!!:D
 
After much ado about trivial stuff, finally got my Sierra software.

Gonna run it versus Bergers for the same bullet at one muzzle velocity and environment to see what the differences are.
 
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