Talk:Ballistic coefficient

message: Why use "w" for mass? (Perhaps m would be better)
:The truth be known: "w" is the the correct notation. Weight is not the same as mass. Mass is the amount of matter within an object. Weight is a measurement of gravitational pull on said object. Here on earth it is 9.80665 m/s^2 (32.174049 m/s^2). When speaking of the sectional density or density of a projectile the correct term within the equations of sectional density or pounds per square inch (pressure), is the measurement of weight not mass. However, engineers and scientist, as a matter of "connivance", just use "mass". Greg Glover (talk) 16:48, 14 August 2014 (UTC)
replies: text: The "d" found in the sectional density equation as d^2 is not "diameter". "d" is the correct notation for distance. d is equal to: SI in meters; Metric in centimeters and Imperial units in inches. The meaning of cross section is a measurement across the width of the body. It just so happens that the diameter of a bullet is also the cross section. Sectional density is not equal to pressure. Pressure is an measurement of area. Sectional density is an absolute value (loosely, as stated above, an equality). Greg Glover (talk) 17:01, 14 August 2014 (UTC)
thread_title:  Equation oddities 

message: Would it make sense to add a section discussing rocket launches? Isn't the reason a rocket is shaped like a bullet because that optimizes the ballistic coefficient? Also, in both cases is there a tie-in with the center of gravity/center of propulsion concept that could be covered? Sdsds 18:56, 26 March 2007 (UTC)
replies: text: The main reason a lot of launch vehicles are tall and narrow is for transportation reasons. If they made the vehicle wider then they wouldn't be able to deliver it from the factory to the launch site. Other than that, aerolosses during ascent are inversely proportional to ballistic coefficient, which in turn is essentially proportional to vehicle length. For a dense-fuelled vehicle about 20m long there are roughly 300 m/s losses. For liquid hydrogen stages, the vehicles need to be proportionately longer, because the density of the vehicle is lower.WolfKeeper 19:45, 26 March 2007 (UTC)
thread_title:  Launch vehicles 

message: This description of the general aerodynamic concept of the "Ballistic Coefficient" seems very strongly pointed toward the sub-genre of projectile ballistics. Suggest moving all the rifle+bullet stuff to another article (perhaps referenced as application examples) so the basic concept can be clearly seen, out of any clutter. With a good understanding of the basic concept, all the bullet observations should make sense. I'm not so sure you can easily go from a laundry list of interesting bullet trajectory observations to an understanding of the basic concept, however. Matt in tx (talk) 05:43, 6 February 2008 (UTC)
replies: text: I concur. It reads like a physics article hijacked by gun nuts. Bomazi (talk) 03:39, 16 October 2012 (UTC)
thread_title:  Entire thrust of the article too pointed toward projectile ballistics? 

message: Wouldn't a higher BC reduce heat during entry into earth's atmosphere?  —Preceding unsigned comment added by 71.112.78.96 (talk) 23:24, 31 March 2008 (UTC)
replies: text: Nah. It takes longer to slow down.- (User) WolfKeeper (Talk) 01:12, 1 April 2008 (UTC)
thread_title: Heat during reentry

message: It would be nice to see some examples of how they are to be used. For instance, calculate the BC of a bullet or an airgun pellet. 87.59.100.37 (talk) 12:37, 16 July 2008 (UTC)
thread_title:  The formulas are good but we need to know how to use them 

message: Using lbs & in vs. m & kg changes things drastically. Also, the sectional density/i and M/A/Cd versions are not interchangable whatsoever. From what I can tell, the sectional density variant (with rectangular area instead of circular) is the one commonly used. There is no explanation for what 'i' is. It's not the coefficient of drag, and it's not the coefficient of drag*pi, so what is it? I'd edit this myself but the information isn't as easy to find as I'd like. I can't find it on the internet (yet).  —Preceding unsigned comment added by 98.240.227.220 (talk) 05:00, 17 September 2008 (UTC)
replies: text: The observation that imperial and metric units changes things drastically is right. To avoid very large or small numbers metric units can be easily manipulated by using larger or smaller decimal subunits. In that regard metric units are very handy. In small arms related topics I have never encoutered BC (the SD could be presented in metric units) being expressed in metric units. BC is normally presented to its reader as a dimensionless quantity. The form factor "i" is like the drag coefficient a dimensionless quantity. At http://www.eskimo.com/~jbm/topics/secdens.html you can read something about the units commonly used and see BC is presented as a dimensionless quantity. Maybe it is better to remove the units section in the articles introduction and point out imperial units are normally ussed in samll arms related contexts for expressing the SD. Now the article communicates to its reader: dimension X = (dimension X / dimensionless quantity).--Francis Flinch (talk) 07:15, 17 September 2008 (UTC)

text: FYI Ballistics isn't just the study of bullets, and Ballistic coefficient doesn't just apply to bullets either. Missiles and spacecraft are usually described as also having ballistic coefficients, but the theory behind it is also useful for describing cars, aircraft etc. etc.- (User) Wolfkeeper (Talk) 00:40, 6 November 2008 (UTC)
thread_title:  Need some elaboration on units 

message: The following formula in addition to other highly useful is offerd at http://www.docstoc.com/docs/3424351/A-Very-Simple-Guide-To-the-Ballistic-Coefficient-with-particular
Allowing bc to be used similar to the formulas here except accounting for air resistance http://en.wikipedia.org/wiki/Trajectory_of_a_projectile 
BC = (R1 - R0) / Loge(V0 / V1)*8000)
where: 
BC = Ballistic coefficient 
R0 = Near range (yards)
R1 = Far range (yards)
V0 = velocity at R0(Ft/s2)
V1 = velocity at R1(Ft/s2)
Is this correct and does anyone have a SI version with meters rather then yards 
:Instead of 8000 use 7315 (with the ranges measured in metres). Be aware though that the above expression is based o the constant Cd model (Cd = 0.205 approx.) and is not particularly/acceptably accurate for any known practical application.GPConway (talk) 12:31, 12 January 2015 (UTC)
replies: text: This is how you find the drag coefficient of any object including the G1 model.  It's fairly straight forward and comes directly from a free body diagram for an object traveling in the x-axis.  (Bullets only) After you find the drag coefficients for both bullet and G1 model, you compare the bullet's drag coefficient to the G1 model's to get the form factor i in the equation in the above section
Fd=Force of drag (N)
M=mass (kg)
ax=acceleration in the x-axis (m/s^2)
\rho=density of air (kg/m^3)
v=velocity (units aren't important because you will be making a ratio of final vs initial velocities) 
C=coefficient of drag (unitless)
A=cross sectional area (m^2)
\sum F_x=Ma_x
-F_d=Ma_x; F_d=.5 \rho\ v^2CA
-.5 \rho\ v^2CA=Ma_x
\frac{-.5 \rho\ v^2CA}{M}=a_x; a_x=v \frac{dv}{dx}
\frac{-.5 \rho\ v^2CA}{M}=v \frac{dv}{dx}
dx=\frac{-2M}{\rho\ vCA}dv
\textstyle \int\limits_{x_1}^{x_2}\,dx=\frac{-2M}{\rho\ CA} \textstyle \int\limits_{v_1}^{v_2} \frac {1}{v}\,dv
\Delta x=\frac{-2M ln(\frac{v_2}{v_1})}{\rho\ CA}
C=\frac{-2M ln(\frac{v_2}{v_1})}{\rho\ \Delta x A}
Gulielmi2002 (talk) 21:36, 23 November 2009 (UTC)
replies: text: The above equations are for the application of actual projectiles. G1 or for that matter any Standard Model has a BC of 1. The original one inch, one pound, lead projectile was a reference on a piece of paper. It never really existed. As a matter of fact the original "one pounder" was not one pound. It was a metric measurement in centimeters and grams. The conversion was made by  LtCol. James Monroe Ingalls. Greg Glover (talk) 16:22, 14 August 2014 (UTC)
thread_title:  G1 more formulas  

message: Example:
"Sporting bullets, with a calibre d ranging from 0.172 to 0.50 inches (4.50 to 12.7 mm), have BC’s in the range 0.12 to slightly over 1.00"
Ok, stop right there.  A BC of 1.0?  You know, the very intro of this article notes that BCs may be given in different units.  The references I can check for these are all dead too.  This is... particularly egregious.  -Theanphibian (talk • contribs) 20:57, 5 June 2011 (UTC)
replies: text: lb/in² added to text.--Francis Flinch (talk) 11:06, 16 October 2012 (UTC)
replies: text: It doesn't matter. i (Coefficient of form) is always 1.00 for any "G" Model reference; that includes G7. All G7 exterior ballistics are computed using integrated number model that includes the mach number. It is a different computation than the original G1 retardation model. However any "G" Model i can be converted to be used in any type of trajectory model computation for exterior ballistic computations. BC and the type of mathematical analysis used to compute the resulting exterior ballistic  are really two different animals.  Edited Greg Glover (talk) 03:11, 23 August 2014 (UTC)

text: Form Factor = your bullet's drag / drag of a standard bullet (say the G7 standard bullet)  — Preceding unsigned comment added by 72.188.56.99 (talk) 17:36, 23 March 2014 (UTC)
replies: text: I'm gonna clean this misconception up by giving an expanded explanation of the "G" Models.Greg Glover (talk) 18:32, 24 August 2014 (UTC)
thread_title:  Can we please use units when giving actual examples? 

message: I added the paragraph from the Reference Notes for Use in the Course in Gunnery and Ammunition, Coast Artillery School, pg12 to stop the implication that the G1 Standard Model shape and/or Friedrich Krupp AG used/was an actual; 1 inch, 1 pound projectile with either 1 1/2 or 2 caliber tangent ogive.
If indeed someone thinks that there was such a "test" projectile used by Friedrich Krupp AG between between 1865 to 1930. Please post your reference for review before deleting my reference that it was a "factitious" model not an actual projectile. Thank you, Greg Glover (talk) 18:00, 13 August 2014 (UTC)
thread_title: The "One Pounder" is Factitious

message: I'd like to start a conversation as to were this Article is going. I remember back sometime ago. This article was very clean if not to specific. But I do remember when there was a difference between Ballistic Coefficient equations and denoted as such with the subscript physics and ballistics. I see the subscript for physics still exists.
I understand why article is devoted to smallarm projectiles. Ballistic coefficient is a sub set of Physics known as "drag"; specifically Drag Coefficient. The Article does not seem to explain this. As pointed out above, but conflated, drag affects; bullets, rockets, missiles, cars, aircraft, etcetera. However a ballistic coefficient in its purest form is specific to projectiles not under power. Those projectiles or presented surfaces, under power are then referred to as just having a "drag coefficient". Hence this article is really a stub of Drag Coefficient.
What say you?
Greg Glover (talk) 17:25, 14 August 2014 (UTC)
replies: text: No, drag coefficient and ballistic coefficient are related, but are not the same thing, so need not be in the same article. Nevertheless you could cover them in one article, since they're related, but the article would be too big, as they are right now, they're good sizes.GliderMaven (talk) 22:48, 15 August 2014 (UTC)
replies: text: I'm sorry, apparently I was not clear. but you did understand my greater point. Yes, "drag coefficient and ballistic coefficient are related". My point was that drag is the greater discussion as covered by drag coefficient within physics. And is covered well in that article. But here on Ballistic coefficient the article seems to pull in concepts of drag and plan presentation to drag. As well as mixing Standard Model drag reference with actual bullet drag calculations. I'm thinking maybe the top part needs to be cleaned up and straightened out. But excellent point GliderMaven Greg Glover (talk) 18:28, 16 August 2014 (UTC)
thread_title: Ballistic Coefficient: '''Physics''' and '''Ballistics'''

message: ====Things Done====
*The equation for BC moved up to Formula. Section Formula renamed to Formulae. More formulas and solid references added. 21 AUG 14 Greg Glover (talk) 16:04, 23 August 2014 (UTC)
thread_title: First Revision

message: *The equation for BC moved up to Formula. Section Formula renamed to Formulae. More formulas and solid references added. 21 AUG 14 Greg Glover (talk) 16:04, 23 August 2014 (UTC)
thread_title: Things Done

message: ====Things done====
*Bullet performance section reformatted. No changes to text. 24 AUG 14 Greg Glover (talk) 19:06, 24 August 2014 (UTC)
thread_title: Second Revision

message: *Bullet performance section reformatted. No changes to text. 24 AUG 14 Greg Glover (talk) 19:06, 24 August 2014 (UTC)
thread_title: Things done

message: This sentence ...
"Circa 1665, Sir Isaac Newton derived the law of air resistance and stated it was inversely proportional to the air resistance."
is techno-babble. It is unclear what it should say.
Perhaps somebody (preferably with access to the cited references) can figure out what it is supposed to be saying and correct it.
 87.115.82.105 (talk) 16:28, 26 October 2014 (UTC)
thread_title:  Background - revision request 

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message: "G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets)"
Try to make a 10 * caliber radius tangent with the dimensions provided, it won't work.  A secant could do it though.
2600:1700:8830:8DF0:D1A1:40AD:68C8:C482 (talk) 06:12, 13 August 2018 (UTC)
replies: text: In my research, I found this source, confirming my assumption: SBT STANDARD PROJECTILE
2600:1700:8830:8DF0:942E:50F1:92B5:DB20 (talk) 08:11, 14 August 2018 (UTC)
thread_title:  G7 claims to be a tangent ogive when it is geometrically a secant ogive