This situation is mitigated somewhat by the fact that aerodynamic drag on a bullet diminishes dramatically in the lower transonic and subsonic velocity regions. Consequently, the effect of large ballistic coefficient errors on bullet trajectories is much less than when the bullet velocities are above fps. For handgun bullet trajectories, the effect is also lessened by the fact that ranges to the targets or the game animals are considerably shorter than for rifles.
But at the present time, accurate long-range trajectories simply cannot be calculated for bullets that travel at lower transonic and subsonic velocities. This is an area of continuing research for these authors.
Ballistic coefficient data have been gathered for a variety of rifle and handgun bullets at transonic and subsonic velocities. Investigations are under way to find modifications to the G1 drag function at velocities below fps that will enable ballistic coefficients to remain reasonably constant in this velocity region.
We hope to be able to report successfully on this research effort at a later date. The G1 drag function is the best standard drag model to use. We have tested several drag functions G1 for sporting bullets; GL for lead bullets; G5 for boat tail bullets; and G6 for flat base, sharp pointed, fully jacketed bullets. For each drag function we have measured BC values referenced to that function and observed how those BC values change with bullet velocity.
We have chosen G1 because the changes in BC values with bullet velocity are least, and because there is a vast database in the literature on BC values referenced to the G1 standard. Also, to our knowledge all projectile manufacturers refer their published BC values to the G1 drag function, which facilitates comparisons among bullets of different calibers, weights, shapes and manufacturers. Any of the firing test methods measures a ballistic coefficient of the bullet as it flies through the air, including effects imparted by the gun, the cartridge, and firing point environmental conditions, as well as imperfections in the bullet.
Theoretically, the BC of a bullet depends only on its weight, caliber and shape. But in a practical sense, the measured BC of a bullet also depends on many other effects. The GS model is for perfect spheres, and could be used for musketballs and BBs, however very few ballistic calculators support it. This model is designed for heeled bullets commonly used in rimfire rounds like the. It is rarely used. For a given bullet, its ballistic coefficient as matched with an appropriate model can be calculated via the formula below:.
We will discuss form factor in a later post, but the important thing to know now is that form factors are not universal. An i7 Form Factor value only works with the G7 ballistic coefficient; you need to use a different form factor for a different ballistic model. Unlike many other calculators, it properly accounts for the reduction in wave drag that comes as a projectile loses speed, especially in the transonic and subsonic flight regimes.
Plus, it has by far the most options of any free calculator I have used. If you are interested in doing your own calculations, I have over the past several years collected and created ballistic coefficient figures for various projectiles, the list of which you can find in a spreadsheet over at my blog. It is based on a list originally collated by Fr. I do know that for my spreadsheet, much of the original work was done by Brian Litz, so many thanks to him.
The Firearm Blog is a news site dedicated to all things firearms related. TFB covers top stories in the firearms industry. TFB staff writers share a passion for firearms but come from a diverse background, stretching from the world of law enforcement to being deployed on the streets of Fallujah, Iraq to the woods hunting wild game. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point.
At the other end of the bullet, a boat tail or tapered heel reduces drag compared to a flat base. Both increase the BC of a bullet. For example, a Hornady grain round nose 6mm bullet has a BC of. All three of these bullets have a sectional density which is the ratio of a bullet's diameter to its weight of. But the more streamlined bullets have a higher ballistic coefficient.
They are the ones to choose for long range shooting where a flatter trajectory is important. To illustrate the practical difference between these three styles of bullets, let's use Hornady's trajectory figures for the grain 6mm bullets above.
Starting all three bullets at a muzzle velocity of fps from a scoped 6mm rifle zeroed at yards, the trajectories are as follows. In the reference projectiles for each standard coefficient, the aforementioned form factor i is equal to 1. Many bullet manufacturers today publish the G1 and G7 BCs for their bullets, as they are the most commonly used ones. Storm Chasing Storm Chaser Kit.
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