Ballistic Coefficient

[ChrisF]

How can I find the ballistic coefficient ofvthe 535gr money bullet. And what do the numbers mean when you find out what they are? Not good with math.

[SchuetzenDave]

Here is a link to a discussion on the basics of ballistic coefficients:

https://everipedia.org/wiki/Ballistic_coefficient/

[bruce m]

chris,
make yourself familiar with JBM calculations website.
the trajectory calculations are what you need.
then you will need a muzzle velocity and 3 sight settings at say 100, 300, and 500 yds.
more is better, and the further the better.
you need to know your sight radius to calculate exactly how moa relates to your points on the sight.
now you can create trajectories on JBM with adjusted b.c. until you get one to match.
use the g1 drag model, as while it is not perfect for our bullets it is close.
your bullet will probably come in the high 0.4s and possibly 0.5.
i gave some bullets to a ballistician, and his calculations came in the mid 0.3s which was way out.
shooting with 2 chronos at the muzzle and 100 yds will also enable calculations, but this method also gives lower b.c. than reality.
i suspect it is because at that distance our bullets are in the top end of transonic velocities when drag is extremely high.
the b.c. calculated thus is true for that velocity range, but not for average.
things that affect b.c. include alloy hardness givind different ammounts of nose slump, and the size of grease grooves or whether there are grooves or not.
keep safe,
bruce.

[ChrisF]

Sounds very difficult for someone not good in math

[bruce m]

chris,
all you need to understand mathematically is that the bigger the b.c. number, the better the bullet slips through the air.
god made computers for us mathematically challenged guys.
the more slippery the bullet, the less drop it has for a given muzzle velocity.
and more importantly the less the bullet loses velocity, the less wind deflection .
the big advantage of this thing is that you can generate wind charts to predict wind deflection.
keep safe,
bruce.

[gunlaker]

Chris, I shoot a number of different Money bullets, from BACO and Paul Jones. Start with 0.5 as the ballistics coefficient and enter your information into the free online calculator at JBM Balllistics. Your sight settings will be quite close, but you want to pay attention to the altitude and temperature of the range at which you will be shooting. You do not need to be good at math to use their free calculator . Their numbers will be a little less good past 800 yards ( but generally not out by more than 5 or 6 minutes if you do it right ) but certainly a great starting point when you head to a match at an unknown range with do data.

Chris.

[bruce m]

some further thoughts on this subject.
there is an unnoticeable difference in deflection between a b.c. of say 0.46 and 0.48.
there is a noticeable difference between 0.4 and 0.5.
the further you shoot, the more b.c will be your friend.
harder alloys retain nose shape better and therefore have higher b.c.
high b.c. is worthless if the bullet will not group.
when hunting, b.c. is of little importance compared to terminal performance.
in part this is due to ranges being shorter, but also killing effect is the primary concern.
nose shapes with good killing effect usually have more drag than a long range target bullet.
the fact that our bullets have lowest b.c. at the muzzle or close to due to highest drag in the transonic zone means that we need to be particularly mindful of the wind at closer ranges, as they deflect more for the same wind there.
keep safe,
bruce.

[TexasMac]

Here's an excellent tutorial from Sierra Bullets on ballistic coefficient & the problems with attempting to determining the BC with standard formulas. BTW, I was not aware of how much the BC is affected by velocity, especially at the typical BPCR velocity ranges.

http://www.exteriorballistics.com/ebexp ... 5th/24.cfm

Wayne

[SFogler]

I use the Hornady ballistics calculator with a nominal .4 BC and nominal velocity of 1250 for lighter loads and 1300 for heavier loads. (I don't have a working chrony.) The predicted results are very close to my observed results when I go out and actually shoot the rifle to get confirmed sight settings. Close enough to get on paper at what ever range I want settings for and refine from there. The BC I use came from noting the most commonly quoted BCs talked about in the forums. I don't do math either; I just want to get sight settings for a new rifle or sight without using up all my ammo.

[bruce m]

wayne,
there is also the yaw of repose, a yaw that the bullet settles into after precessation and nutation.
the big dilemma with this yaw is that the faster the twist, the more the yaw.
for long range long bullets are better, but they require faster twists.
the greater tha yaw of repose, the greater is spindrift, and b.c. is reduced.
keep safe,
bruce.

[John Boy]

A couple of links that do the actual calculation - not just the formula ...

http://gundata.org/ballistic-coefficient-calculator/

http://www.handloads.com/calc/index.html

[Jim Kidwell]

ChrisF,
Just curious. Now that you have your BC of your 535gr money bullet, what are you going to do with it? How many moulds are you comparing it with? We are shooting BPCR not Bench Rest or Palma.................

[CO]

jim Kidwell, I would never think of loading a bullet without knowing it's ballistic coefficiency.

Co

[bruce m]

forget both of johnboy's links.
too simplistic and not close to reality.
jbm is still the best, and it also calculates.
keep safe,
bruce.

[bruce m]

co,
you would suddenly get an interest in this if someone started winning because of a higher b.c. bullet.
look at dave gullo when he dropped the paul jones (so called) creedmoor in favour of the money bullet.
keep safe,
bruce.