Range Report Ballistics Notation Question
- Thread starter Crisisman
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Re: Ballistics Notation Question
My guess would be the BC's are for High, Medium, and Low speed. This would be a poor way to define BC though, you really need to know the velocity. Maybe there's a help file with the source that says what numeric velocities correspond to H, M and L.
-Bryan
My guess would be the BC's are for High, Medium, and Low speed. This would be a poor way to define BC though, you really need to know the velocity. Maybe there's a help file with the source that says what numeric velocities correspond to H, M and L.
-Bryan
Re: Ballistics Notation Question
Was thinking that same but would seem wrong based on the fact that there has to be a FPS reading to say from this speed to this speed you have this BC. And Bryan I know you know that the speed has to be posted to get accurate readigs versus hi, med, and low.
Was thinking that same but would seem wrong based on the fact that there has to be a FPS reading to say from this speed to this speed you have this BC. And Bryan I know you know that the speed has to be posted to get accurate readigs versus hi, med, and low.
Re: Ballistics Notation Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body"> This would be a poor way to define BC though, -Bryan </div></div>
Isn't the whole concept behind the BC poor? Why use reference shapes at all?
tob
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body"> This would be a poor way to define BC though, -Bryan </div></div>
Isn't the whole concept behind the BC poor? Why use reference shapes at all?
tob
Re: Ballistics Notation Question
I got my answer. Apparently they are velocity ranges. I'm no Aerodynamics expert, so I don't understand why drag changes at various velocities, perhaps with the sound barrier? Anyhow, now I know how to use the info. Thanks.
I got my answer. Apparently they are velocity ranges. I'm no Aerodynamics expert, so I don't understand why drag changes at various velocities, perhaps with the sound barrier? Anyhow, now I know how to use the info. Thanks.
Re: Ballistics Notation Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">My guess would be the BC's are for High, Medium, and Low speed. This would be a poor way to define BC though, you really need to know the velocity. Maybe there's a help file with the source that says what numeric velocities correspond to H, M and L.
-Bryan</div></div>
From what I understand this appears to be the case. Sierra (I have no idea about other companies) seems to have H as 2800 and higher, M as 1800-2800 FPS and L as being 1800 and below.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">My guess would be the BC's are for High, Medium, and Low speed. This would be a poor way to define BC though, you really need to know the velocity. Maybe there's a help file with the source that says what numeric velocities correspond to H, M and L.
-Bryan</div></div>
From what I understand this appears to be the case. Sierra (I have no idea about other companies) seems to have H as 2800 and higher, M as 1800-2800 FPS and L as being 1800 and below.
Re: Ballistics Notation Question
I figured that's what it is but its a poor way to put it based on the fact that there is no number of FPS associated with it. I take it as the bullet travels through various stages of speed the BC changes because speed is falling and so is the BC. Just my 2 cents.
I figured that's what it is but its a poor way to put it based on the fact that there is no number of FPS associated with it. I take it as the bullet travels through various stages of speed the BC changes because speed is falling and so is the BC. Just my 2 cents.
Re: Ballistics Notation Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Crisisman</div><div class="ubbcode-body">I got my answer. Apparently they are velocity ranges. I'm no Aerodynamics expert, so I don't understand why drag changes at various velocities, perhaps with the sound barrier? Anyhow, now I know how to use the info. Thanks. </div></div>
This is why:
Drag varies greatly with velocity. The shape of that curve is standardized so that you can scale it to your bullet if you know it's BC, which is a scaling factor that is not supposed to change with velocity. This works well when the shape of the standard drag function matches that of your actual bullet well.
But the common G1 drag function is such a poor fit to the actual drag profile of long range (boat tail, large ogive) bullets, that the bullet makers have to correct for this by changing the BC as velocity changes. It's nothing more than a mathematical kludge.
The proper way to do it is to use a drag function that has the same shape as the drag profile of your bullet. For long range bullets, that generally means G7. This way, BC will not vary (significantly) with velocity. That's the way it's supposed to work. The wrinkle is that almost nobody publishes G7 BC's (which are not the same as the typically published G1 BC's). Bryan's book is the first major commercial effort to do so that I'm aware of.
So why not just do away with this standard drag function/BC business and just measure the drag profile of every bullet? It's insanely expensive. The military does that. That's why we know so much about the 168gr MatchKing, for example. They've studied the crap out of it.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Crisisman</div><div class="ubbcode-body">I got my answer. Apparently they are velocity ranges. I'm no Aerodynamics expert, so I don't understand why drag changes at various velocities, perhaps with the sound barrier? Anyhow, now I know how to use the info. Thanks. </div></div>
This is why:
Drag varies greatly with velocity. The shape of that curve is standardized so that you can scale it to your bullet if you know it's BC, which is a scaling factor that is not supposed to change with velocity. This works well when the shape of the standard drag function matches that of your actual bullet well.
But the common G1 drag function is such a poor fit to the actual drag profile of long range (boat tail, large ogive) bullets, that the bullet makers have to correct for this by changing the BC as velocity changes. It's nothing more than a mathematical kludge.
The proper way to do it is to use a drag function that has the same shape as the drag profile of your bullet. For long range bullets, that generally means G7. This way, BC will not vary (significantly) with velocity. That's the way it's supposed to work. The wrinkle is that almost nobody publishes G7 BC's (which are not the same as the typically published G1 BC's). Bryan's book is the first major commercial effort to do so that I'm aware of.
So why not just do away with this standard drag function/BC business and just measure the drag profile of every bullet? It's insanely expensive. The military does that. That's why we know so much about the 168gr MatchKing, for example. They've studied the crap out of it.
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