Cast Bullet BC's

[thirtythirty]

Hello. I am contemplating (yet another) mold purchase. (They are accumulating at a disturbing pace :P ). This one is is for my Mosin. I was looking at Lee's lineup and the accompanying BC's. The BC's are whats confusing me. The lee .309-180 has a BC of .317, but the 312-185 (looks very similar?) has a much lower BC of .247. What is the cause for this dramatic difference? I'm hoping to shoot at a little bit longer ranges (200ish+ yds), and am therefore hoping to get a bullet which won't drop stupid amounts. However, if the BC of the 312-185 is .247 than I might forgo it and just PP my .309-170 as its BC is .268.

Thanks for your help!

[rancher1913]

familiar with PB molds and GC molds but drawing a blank on what a BC mold is.

[Tom Myers]

familiar with PB molds and GC molds but drawing a blank on what a BC mold is.

BC = Ballistic Coefficient

[Larry Gibson]

BCs (Ballistic Coefficients) are mostly derived from computer programs based on the bullet drawing. There are many things that can adversely affect the actual BC of the bullet in flight.......the computer programs do not take those into account. Mostly the computer generated BCs are overly optimistic. How do I know that(?)......because I can measure the time of flight between the muzzle and a 100 yards target and the Oehler M43 automatically computes the actual BC of each bullet. The newer Doppler radar chronograph also accurately measures BCs. However, some published BCs are from actual measurements (usually TOF and velocity lost between muzzle and a distance down range) and are close. Keep in mind that each bullet fired will not have exactly the same BC. Just as with FPS there will be a variation of BCs in any test string. If you have a good load with a 10 shot ES of 50 - 60 fps or less the BCs will also be very close so the "average" BC will do for trajectory calculations.

I have tested the Lee C312-185 out of my own MN and the listed BC is close. The Lee C312-185 is an excellent bullet in my MNs with .312 and .313 groove diameters. However the Lyman 314299 and the NOE 314-299 are just as accurate at 100 and 200 yards (I use them in CBA matches) and are better at longer ranges as both do have a better BC.

FYI; the Lee C309-XXX moulds may not cast bullets large enough in diameter to properly fit the MN bore and groove diameters.

[thirtythirty]

BCs (Ballistic Coefficients) are mostly derived from computer programs based on the bullet drawing. There are many things that can adversely affect the actual BC of the bullet in flight.......the computer programs do not take those into account. Mostly the computer generated BCs are overly optimistic. How do I know that(?)......because I can measure the time of flight between the muzzle and a 100 yards target and the Oehler M43 automatically computes the actual BC of each bullet. The newer Doppler radar chronograph also accurately measures BCs. However, some published BCs are from actual measurements (usually TOF and velocity lost between muzzle and a distance down range) and are close. Keep in mind that each bullet fired will not have exactly the same BC. Just as with FPS there will be a variation of BCs in any test string. If you have a good load with a 10 shot ES of 50 - 60 fps or less the BCs will also be very close so the "average" BC will do for trajectory calculations.

I have tested the Lee C312-185 out of my own MN and the listed BC is close. The Lee C312-185 is an excellent bullet in my MNs with .312 and .313 groove diameters. However the Lyman 314299 and the NOE 314-299 are just as accurate at 100 and 200 yards (I use them in CBA matches) and are better at longer ranges as both do have a better BC.

FYI; the Lee C309-XXX moulds may not cast bullets large enough in diameter to properly fit the MN bore and groove diameters.

Thanks! If I were to use the 309 bullet I would paper patch it up to size. So why does the .309-170 (with a flat nose) have a better BC than a round nose 312-185?

[Larry Gibson]

Where are you getting the BCs from?

[vzerone]

Where are you getting the BCs from?

What BC did you get for both those LEE bullets?

[evoevil]

I used to use the highest BC bullet I could find, But after using the Berger twist rate calculator and found some lower BC bullets shoot better. each gun is different and you still need to play with seating depths and powders. I would not be that worried about it, but Berger Bullets have a lot of information on all of it. You can go to their webpage and put your own ifno in and see what they come up with

[thirtythirty]

Where are you getting the BCs from?

Lee's website.

[vzerone]

Bullet - Ballistic Coefficient
32/20, 32 S& W Long, 32 Colt NP

311-93-1RF- .125
311-100-2R- .174
TL314-85-WC- .054
TL314-90-SWC- .100
38 Special, 38 S&W, 38 Colt New Police

358-105-SWC - .106
358-125-RF - .116
358-140-SWC - .142
TL358-148-WC - .072
358-148-WC - .072
358-150-1R - .131
358-150-SWC - .111
TL358-158-SWC - .117
C358-158-SWC - .117
TL358-158-2R - .207
358-158-RF- .160
9 mm Luger, 38 Super Auto, 380 Auto

356-102-1R - .105
356-111-1R - .114
356-120-TC - .123
TL356-124-2R - .164
TL356-124-TC - .127
356-125-2R - .166
356-153-2R - .203
9mm Makarov

365-95-1R - .093
40 S&W, 10 mm

401-145-SWC - .117
TL401-175-SWC - .141
401-175-TC - .141
41 magnum, 41 AE

410-195-SWC - .110
TL410-210-SWC - .119
TL410-175-SWC - .099
44 Special, 44 Magnum, 44 / 40 WCF

429-208-WC - .070
429-214-SWC - .111
C429-240-SWC - .124
429-255-SWC - .132
429-200-RF - .124
429-214-1R - .151
429-240-2R - .196
TL430-240-SWC - .169
C430-310-RF - .218
45 ACP, 45 Auto Rim, 45 Colt

452-190-SWC - .121
452-200-SWC - .127
452-200-RF - .140
TL452-200-SWC - .127
452-228-1R - .145
TL452-230-2R - .189
TL452-230-TC - .146
452-230-TC - .146
45 Colt, 45 Casull

452-252-SWC - .136
452-255-RF - .210
C452-300-RF - .233
7mm

C285-130-R - .305
30 Caliber Rifle

C309-113-F - .199
C309-120-R - .163
C309-130-R - .229
C309-150-F - .264
C309-160-R - .252
C309-170-F - .268
C309-180-R - .317
C309-200-R - .352
38-55 / 375 Winchester

379-250-RF - .249
7.62 x 39

C312-155-2R - .268
CTL312-160-2R - .276
7.65 - 7.7 mm, 303 British

C312-185-1R - .247
8 mm

C324-175-1R - .216
338 Cal

C338-220-1R - .250
45-70 Caliber Rifle

457-340-F - .211
457-405-F - .225
459-405-HB - .250
457-450-F - .250
C457-500-F - .278
457-500-3R - .443
480 Ruger, 475 Linebaugh

476-400-RF - .271
50-70 Caliber

515-450-f- .220
515-500-f- .283

Round ball coefficients are based on a velocity of 1000 - 1300 f.p.s at the muzzle.

.308 - .038
.311 - .039
.319 - .040
.330 - .042
.350 - .044
.360 - .045
.375 - .047
.380 - .048
.390 - .049
.395 - .050
.433 - .055
.440 - .056
.445 - .056
.451 - .057
.454 - .057
.457 - .058
.490 - .061
.495 - .062
.498 - .064
.500 - .061
.527 - .067
.530 - .067
.535 - .068
.562 - .071
.575 - .072
.600 - .076
.690 - .087
Conical Bullet Molds

36 Cal .375-130-1r - .120
44 Cal .450-200-1r- .128
44 Rug .456-220-1r- .137
Mini Bullet Mold

58 Caliber 575-500- .196
Modern Mini, Target Design

Both sizes are .088

[Larry Gibson]

Lee's website.

Can you be more specific as to where on Lee's site?

What I get from leeprecision.net is; We don't have ballistic coefficients for our bullet moulds. The primary reason is that the percentages of material used in the mold is quite different from one caster to another. Calculating ballistic coefficients are complicated and also involve a form factor. Our Shooter program allows you to calculate it through the use of reading velocity reduction over a given distance.

Have you calculated the BC from Lee's "Shooter program" using the specifics of your bullet?

[Adam20]

Go on lee site, click on rifle molds, The first line under the mold is b.c.

https://leeprecision.com/bullet-cast...-bullet-molds/

[Artful]

http://castboolits.gunloads.com/show...efficent-Table

[Larry Gibson]

What I'm really asking for is how the Lee listed BCs were determined, by computer or by actual tests?

[Artful]

What I'm really asking for is how the Lee listed BCs were determined, by computer or by actual tests?

https://www.titanreloading.com/balli...ients-on-molds

Ballistic Coefficients on Molds

We have used the form factor method of calculating the ballistic coefficients for our bullet molds in conjunction with the formula of C = w / i * (d*d) where C is the coefficient, w is the bullet weight in pounds, i = the form factor and d = the bullet diameter. For the purposes of our calculations, we have assumed that all bullets will have a muzzle velocity of 2000 f.ps. or less. Bullet weights are based on 1 part tin to 10 parts lead.

We do not have ballistic coefficients on all of our black powder molds as some are larger than .50 caliber and others have a taperd shank such as the REAL bullet. These calculations would result in inaccuracies, therefore it is best to determine those through firing and recording the reduced velocity over a given distance. That data can then be entered into our Shooter program which calculates the ballistic coefficient.

Bullet - Ballistic Coefficient
32/20, 32 S& W Long, 32 Colt NP

311-93-1RF- .125
311-100-2R- .174
TL314-85-WC- .054
TL314-90-SWC- .100

38 Special, 38 S&W, 38 Colt New Police

358-105-SWC - .106
358-125-RF - .116
358-140-SWC - .142
TL358-148-WC - .072
358-148-WC - .072
358-150-1R - .131
358-150-SWC - .111
TL358-158-SWC - .117
C358-158-SWC - .117
TL358-158-2R - .207
358-158-RF- .160

9 mm Luger, 38 Super Auto, 380 Auto

356-102-1R - .105
356-111-1R - .114
356-120-TC - .123
TL356-124-2R - .164
TL356-124-TC - .127
356-125-2R - .166
356-153-2R - .203

9mm Makarov

365-95-1R - .093

40 S&W, 10 mm

401-145-SWC - .117
TL401-175-SWC - .141
401-175-TC - .141

41 magnum, 41 AE

410-195-SWC - .110
TL410-210-SWC - .119
TL410-175-SWC - .099

44 Special, 44 Magnum, 44 / 40 WCF

429-208-WC - .070
429-214-SWC - .111
C429-240-SWC - .124
429-255-SWC - .132
429-200-RF - .124
429-214-1R - .151
429-240-2R - .196
TL430-240-SWC - .169
C430-310-RF - .218

45 ACP, 45 Auto Rim, 45 Colt

452-190-SWC - .121
452-200-SWC - .127
452-200-RF - .140
TL452-200-SWC - .127
452-228-1R - .145
TL452-230-2R - .189
TL452-230-TC - .146
452-230-TC - .146

45 Colt, 45 Casull

452-252-SWC - .136
452-255-RF - .210
C452-300-RF - .233

7mm

C285-130-R - .305

30 Caliber Rifle

C309-113-F - .199
C309-120-R - .163
C309-130-R - .229
C309-150-F - .264
C309-160-R - .252
C309-170-F - .268
C309-180-R - .317
C309-200-R - .352

38-55 / 375 Winchester

379-250-RF - .249

7.62 x 39

C312-155-2R - .268
CTL312-160-2R - .276

7.65 - 7.7 mm, 303 British

C312-185-1R - .247

8 mm

C324-175-1R - .216

338 Cal

C338-220-1R - .250

45-70 Caliber Rifle

457-340-F - .211
457-405-F - .225
459-405-HB - .250
457-450-F - .250
C457-500-F - .278
457-500-3R - .443

480 Ruger, 475 Linebaugh

476-400-RF - .271

50-70 Caliber

515-450-f- .220
515-500-f- .283

Round ball coefficients are based on a velocity of 1000 - 1300 f.p.s at the muzzle.

.308 - .038
.311 - .039
.319 - .040
.330 - .042
.350 - .044
.360 - .045
.375 - .047
.380 - .048
.390 - .049
.395 - .050
.433 - .055
.440 - .056
.445 - .056
.451 - .057
.454 - .057
.457 - .058
.490 - .061
.495 - .062
.498 - .064
.500 - .061
.527 - .067
.530 - .067
.535 - .068
.562 - .071
.575 - .072
.600 - .076
.690 - .087

Conical Bullet Molds
36 Cal .375-130-1r - .120
44 Cal .450-200-1r- .128
44 Rug .456-220-1r- .137

Mini Bullet Mold
58 Caliber 575-500- .196

Modern Mini, Target Design
Both sizes are .088

[Larry Gibson]

Artful

Thanks

[popper]

I go to NOE site and look for a similar design, use his calculated BC. Gets me close.