Bullet density and Ballistic Coefficients
11-17-2009, 01:27 PM
#11
Nontypical Buck
Join Date: Feb 2003
Location: Coralville, IA. USA
Posts: 3,802
Well, that equation is the one manufacturers use to ESTIMATE a bullets BC. The "form factor" variable is the one where manufacturers fudge. It would give a valid relative comparison between two bullets of identical shape, but the BC number won't necessarily conform to real world performance. You have to shoot the bullet to get an accurate MV and another accurate velocity reading downrange (at several distances if using the G1 standard), then, adjusting for atmospheric conditions, the average G1 BC can be calculated. If one uses the G7 standard with boattail bullets, the BC will remain much more constant over the entire velocity range, but the BC number will be smaller compared to the G1 BC. The G1 BC, when applied to bullets with a longer than 2 radius tangent ogive, secant ogive or boattail (which is most of the bullets fired from modern CF rifles), will change (decrease) as the velocity decreases. So a spitzer BT bullet at 3000 fps might have an actual G1 BC of .500, but at 2500 fps the BC may only be .450. At 2000 fps the BC might only be .375. If you use the .500 BC number (which is probably the number published by the manufacturer) in a ballistics calculator to calculate the elevation for a long range shot, you would likely miss low because the G1 BC doesn't remain constant as the bullet loses velocity. The G7 standard is much better for most rifle bullets because the drag model closely matches the G7 standard bullet, meaning that the BC changes very little if at all over the entire flight of the bullet. But manufacturers are reluctant to switch to it because the G7 BC number itself is far smaller than the G1 BC (for example, a Berger .308cal 185gr VLD has a G1 BC of 0.549, but a G7 BC of 0.281, but the G7 BC will give much more accurate to real world results when used with a ballistics program like JBM).
Mike
Mike
11-18-2009, 08:44 AM
#12
Typical Buck
Join Date: Jun 2005
Posts: 604
The reason the lead bullet carries its velocity better is that its additional weight makes it harder too slow down due to higher FT/LBS momentum. So more air resistance is required to stop the object of greater mass.
11-19-2009, 05:31 AM
#13
Spike
Join Date: Feb 2007
Posts: 90
Thanks mike,
However, I'm still not getting anything related to the flight characteristics of 2 different bullets made of materials with differing densities.
Here's a scenario that might help understand the question. Let's assume that we have 2 bullets. One made of lead, one made of copper. They are formed in the same mold, loaded in the same rifle and shot at the same speed. What is the difference? Surely there is something, beyond what a calculator using BC and velocity tells us.
However, I'm still not getting anything related to the flight characteristics of 2 different bullets made of materials with differing densities.
Here's a scenario that might help understand the question. Let's assume that we have 2 bullets. One made of lead, one made of copper. They are formed in the same mold, loaded in the same rifle and shot at the same speed. What is the difference? Surely there is something, beyond what a calculator using BC and velocity tells us.
And if you want to switch it around so that the two bullets weigh the same, then their shape will be different. The copper bullet would be elongated and more aerodynamic, unless of course you wanted to make it a flat based round nose and have the lead bullet be a boat tailed spitzer...
Last edited by jason miller; 11-19-2009 at 05:39 AM.
11-19-2009, 07:05 AM
#14
Nontypical Buck
Thread Starter
Join Date: Sep 2009
Location: West NE
Posts: 1,455
JM,
I understand what you're saying. However, even if we elongated the copper bullet to retain the same mass it's BC suffers. Have you seen the Barnes MRX? It has a dense alloy in the rear of the bullet to give it additional penetration, and a higher BC compared to other plain-copper barnes bullets (it's expensive though
).
I understand what you're saying. However, even if we elongated the copper bullet to retain the same mass it's BC suffers. Have you seen the Barnes MRX? It has a dense alloy in the rear of the bullet to give it additional penetration, and a higher BC compared to other plain-copper barnes bullets (it's expensive though
).
11-19-2009, 01:00 PM
#15
Typical Buck
Join Date: Jun 2005
Posts: 604
JM,
I understand what you're saying. However, even if we elongated the copper bullet to retain the same mass it's BC suffers. Have you seen the Barnes MRX? It has a dense alloy in the rear of the bullet to give it additional penetration, and a higher BC compared to other plain-copper barnes bullets (it's expensive though).
I understand what you're saying. However, even if we elongated the copper bullet to retain the same mass it's BC suffers. Have you seen the Barnes MRX? It has a dense alloy in the rear of the bullet to give it additional penetration, and a higher BC compared to other plain-copper barnes bullets (it's expensive though
).However as the bullets get heavier the copper bullets loose their advantage in form factor because they must be made to be stablilized in standard twist barrels and the bullet length must be limited. This results in a more rounded nose section in order to add mass in the length allowed in a given twist rate. The Form Factor suffers slightly from the relatively blunt nose.
The reason Barnes adds the dense material is to maintain the sleek nose section and still be within a length that can be stabilized. So in heavy bullets 200 - 240 grain 30 cal lead will actually have an advantage in BC potential.
11-19-2009, 03:11 PM
#16
Nontypical Buck
Thread Starter
Join Date: Sep 2009
Location: West NE
Posts: 1,455
SG,
I thought I read somewhere that the length and toughness of the copper led to the requirement of the "triple-shock" bands to reduce bering surface and pressure.
Anyways, let's pretend we have a copper and lead bullet of the same mass. The stabilization and velocity are not limiting factors in our pretend setup. They are both stabilized adequately and are shot at the same speed. They are both of a similar aerodynamic shape, but the copper bullet is obviously longer and sleeker to maintain the equal mass. Under what conditions can we assume that one bullet will be better than the other? Will the lead, with its greater density always have the higher BC? Will its density make up for its less-sleek shape?
I thought I read somewhere that the length and toughness of the copper led to the requirement of the "triple-shock" bands to reduce bering surface and pressure.
Anyways, let's pretend we have a copper and lead bullet of the same mass. The stabilization and velocity are not limiting factors in our pretend setup. They are both stabilized adequately and are shot at the same speed. They are both of a similar aerodynamic shape, but the copper bullet is obviously longer and sleeker to maintain the equal mass. Under what conditions can we assume that one bullet will be better than the other? Will the lead, with its greater density always have the higher BC? Will its density make up for its less-sleek shape?
11-19-2009, 05:48 PM
#17
Typical Buck
Join Date: Jun 2005
Posts: 604
SG,
I thought I read somewhere that the length and toughness of the copper led to the requirement of the "triple-shock" bands to reduce bering surface and pressure.
Anyways, let's pretend we have a copper and lead bullet of the same mass. The stabilization and velocity are not limiting factors in our pretend setup. They are both stabilized adequately and are shot at the same speed. They are both of a similar aerodynamic shape, but the copper bullet is obviously longer and sleeker to maintain the equal mass. Under what conditions can we assume that one bullet will be better than the other? Will the lead, with its greater density always have the higher BC? Will its density make up for its less-sleek shape?
I thought I read somewhere that the length and toughness of the copper led to the requirement of the "triple-shock" bands to reduce bering surface and pressure.
Anyways, let's pretend we have a copper and lead bullet of the same mass. The stabilization and velocity are not limiting factors in our pretend setup. They are both stabilized adequately and are shot at the same speed. They are both of a similar aerodynamic shape, but the copper bullet is obviously longer and sleeker to maintain the equal mass. Under what conditions can we assume that one bullet will be better than the other? Will the lead, with its greater density always have the higher BC? Will its density make up for its less-sleek shape?
This is the case with lighter for caliber bullets.
With the heavy for caliber bullets stabilization requirements will limit length and lead will actually have an advantage. So the answer to which is better depends on the application.
11-19-2009, 06:00 PM
#18
Nontypical Buck
Thread Starter
Join Date: Sep 2009
Location: West NE
Posts: 1,455
Thanks SG,
You've ultimately summarized it: The conditions are not necessarily set, although generally copper bullets have more potential in light-mid weights and those that are primarily concentrated of lead would be the choice at heavier weights. And also, if two bullets are shaped the exact same, the denser one will have the higher BC. Another file is in the brain.
You've ultimately summarized it: The conditions are not necessarily set, although generally copper bullets have more potential in light-mid weights and those that are primarily concentrated of lead would be the choice at heavier weights. And also, if two bullets are shaped the exact same, the denser one will have the higher BC. Another file is in the brain.
11-25-2009, 09:34 AM
#19
Typical Buck
Join Date: Jun 2005
Posts: 604
Gags,
Quit guessing...(please).
Should you be enthralled with faux boolit length,please muse the Lapua Scenar and it's grandiose air-filled nose cone. It's HP nose is stretched,to add copious BC and that increased length mandates reserve twist RPM...despite it's launch speeds being inordinate to it's actual BC value(s).
Do homogenous copper BC's trump cup/core values...as a rule?!!? NOPE...........
Quit guessing...(please).
Should you be enthralled with faux boolit length,please muse the Lapua Scenar and it's grandiose air-filled nose cone. It's HP nose is stretched,to add copious BC and that increased length mandates reserve twist RPM...despite it's launch speeds being inordinate to it's actual BC value(s).
Do homogenous copper BC's trump cup/core values...as a rule?!!? NOPE...........
As one would expect when actual measured numbers were compared to the claimed numbers by knowledgeable shooters the claimed BC was significantly overstated. Measured BC came in at around .459. Keep in mind that the Scenar is a match bullet and its construction is not limited by the integrity demands of the hunting bullet you are comparing it to.
That big hollow area behind the point is just a great engineering solution to overcome the density disadvantage of lead in the lighter bullets without the cost of copper.
If you are comparing match bullets to hunting bullets it is apples and oranges but even at that the lead bullets come up short to the new copper hunting bullets from Nosler.
11-26-2009, 05:33 AM
#20
Banned
Join Date: Nov 2009
Posts: 2
.505 is their claimed and actual BC,though of course atmosphere and temp particulars,do change all BC's every day. The 155 Scenar's supeerklative BC is easy to glean from even a casual glimpse as it's length/profile readily concur. Set it next to 168 or 175SMK's,for conversation. It smokes the newly reconfigured 155 Palma SMK as well. I shoot the Scenar by the jazillion and my elevation erector's have no bias built in.
As an aside,Scenar terminal affects are far more reliable than the oft touted SMK,espoused by the Mall Ninja Faction. The Scenar's faux nosecone,is a simplistic and effective approach to increasing projectile length,while adding a favorable BC profiling to a given weight.
I much prefer V-Max and A-Max upon Critters,to the oft touted NBT. Prefer Scenar's to them as well.
Lapua BC's are spot on,as a minimum.........................
As an aside,Scenar terminal affects are far more reliable than the oft touted SMK,espoused by the Mall Ninja Faction. The Scenar's faux nosecone,is a simplistic and effective approach to increasing projectile length,while adding a favorable BC profiling to a given weight.
I much prefer V-Max and A-Max upon Critters,to the oft touted NBT. Prefer Scenar's to them as well.
Lapua BC's are spot on,as a minimum.........................