What is 'Ballistic Coefficient'? Fundamentals of the G1 and G7 Standards
- 20 Mar, 2018
There are many things that go into the production of a bullet; from grain weight to shape all of the engineering that goes into bullets is quite fascinating. One term that is brought up when discussing bullets is ballistic coefficient (BC). For some people this term might be a foreign language, but chances are if you’re a long-range shooter you’ve heard of this expression before. A sniper or long-range hunter may have heard of ballistic coefficients before, because it in essence is a form of measurement that helps calculate the effectiveness of how a bullet travels. In other words ballistic coefficient is the measure of a bullet’s ability to travel or slice per say through the air. It measures just how well a bullet can overcome the air resistance it is flying through in the atmosphere. Essentially the higher the ballistic coefficient number the less the drag of the projectile, resulting in a bullet that will cut through the air more effectively. With just that information alone it is still nearly impossible to truly understand ballistic coefficients without diving more into the subject.
To begin lets examine the actual mathematical formula for ballistic coefficient. Taking the mass of the object, dividing by the bullet’s diameter in the airflow squared; and then dividing by the form factor that relates to the bullet’s shape will help you determine the ballistic coefficient. The caveat here is the bullet’s shape; as many of us know or have seen at sporting good stores there are a variety of bullets with different shapes and sizes. This is what makes calculating the ballistic coefficient a bit more challenging, as there is no solitary perfect formula that works for every bullet.
However there is still hope thanks to a cheat sheet if you will on the different forms and shapes of certain bullets. The two most common terms you will run into are G1 and G7 drag functions. The G1 standard is an older standard that is not necessarily as accurate of a BC measure for today’s bullets because it does not take into consideration the complete trajectory of the bullet overtime. Meaning you might be on at 500 yards but off at a 1,000 yards. This is where the G7 Standard comes into play, the G7 standard is more constant over the flight of the bullet so it does not matter as much in regards to what your BC is at from one distance to another.
G1 projectiles are flat based bullets such as spritzer bullets, where G7 projectiles are going to cover boattail spitzers. In regards to their BC a spitzer bullet has a high coefficient and is suitable for long-range shots, and the boattail spitzer is even superior making it one of the best bullets for long-range targets exceeding 1,000 yards. Another common bullet is a hollow point; hollow points are a form of boattail however they have a much lower BC then the spitzer or boattail spitzers, because of the expansion produced when fired. There are also just plain hollow points and boattail hollow points; a regular hollow point as discussed before will have the lowest BC because of the hollow cavity. One last popular bullet is the round nose, and as the name depicts the bullet is rounded on the end making it similar to the hollow point in regards to a lower ballistic coefficient.
Concluding thoughts on ballistic coefficients is if you are a long-range shooter: BC is something you should use and understand to ensure the best accuracy; a 6.5 creedmor or other boattail spitzer bullets would be an ideal starting place. On the other hand if you do not take long shots; say your shooting at 200 yards and in the BC may not be as big of a concern for you as at that distance the wind deflection and trajectory will not have that big of an impact on the bullet. Lastly there are many different calculators on the market today to help you calculate the BC without having to pull out your calculator. Gun data has nice calculator for getting your feet wet in ballistic coefficients. JBM also has a more in depth calculator that takes into consideration time, velocity, and trajectory.
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