ballistic coefficient of 45-75 bullet

[coyote nose]

Anybody know it or how to figure it out for the Lyman 457122?? It is a HP, but I plugged the mould so it casts as a solid. Does that change the ballsitic coefficient? Does the alloy (ie: weight change) make a difference, or is it just a function of length and diameter??

[Idiot]

Weight and diameter affect Sectional Density. Weight, diameter, bullet shape and construction (hollow point verses spire point, etc.) affect Ballistic Coefficient.

Sectional Density can be a measurement of penetration when comparing simple cup and core bullets with each other. Since Sectional Density does not account for bullet construction, it is a poor tool to use to determine penetration of modern bullet designs or cast bullets.

Ballistic Coefficient helps measure trajectory and terminal velocity (which effect penetration, kinetic energy, etc.) and is a fairly useful tool in estimating bullet flight. I think Handloads.com has a Ballistic Coefficient program that may be useful to you.

Now, the 45/70 Government is not a cartridge that lends itself to flat trajectory. So, I don't think that you've altered your bullet's Ballistic Coefficient much at all by going from a hollow point to a solid. If anything, you've probably improved its trajectory. So instead of the bullet dropping to the ground at 150 yards, it will instead drop at 151 yards.

[coyote nose]

Thanks Idiot. I need the BC for a ballistics program I got out of a 1980's era American Rifleman magazine. Have been using it for years and it really does a good job predicting trajectories. The newer computer ones seem to baffle me. Is there a way i can figure the BC since I have bullet length, shape, diameter and weight? Heading into work now, I'll check the program you mentioned when i get home from work. just was wondering if anybody out there already knew the BC of that bullet.

[Hobie]

Thanks Idiot. I need the BC for a ballistics program I got out of a 1980's era American Rifleman magazine. Have been using it for years and it really does a good job predicting trajectories. The newer computer ones seem to baffle me. Is there a way i can figure the BC since I have bullet length, shape, diameter and weight? Heading into work now, I'll check the program you mentioned when i get home from work. just was wondering if anybody out there already knew the BC of that bullet.

I don't know but I want to. Let me do some research, too.

Sectional Density...
The sectional density of a .45ACP 230 grain bullet is determined as follows:

M
7000 ÷ d2 = sectional density

Step 1:
Divide M (M = bullet weight in grains) by 7000: 230 ÷ 7000 = 0.033

Step 2:
Determine d2 (d2 = the square of bullet diameter in inches): 0.451 x 0.451 = 0.203

Step 3:
Divide the quotient of step 1 by the product of step 2: 0.033 ÷ 0.203 = sectional density of 0.163

The formula for calculating the ballistic coefficient for a bullet is as follows:[1][2]

BC = \frac{SD}{i} = \frac{M}{i \times d^2}

where:

* BC = ballistic coefficient
* SD = sectional density, SD = mass of bullet in pounds or kilograms divided by its caliber squared in inches or meters; units are lb/in2 or kg/m2.
* i = form factor, i = drag coefficient of the bullet/drag coefficient of G1 model bullet (G1 drag coefficient = 0.5190793992194678)
* M = Mass of object, lb or kg
* d = diameter of the object, in or m

This BC formula gives the ratio of ballistic efficiency compared to the standard G1 model projectile. The standard projectile originates from the "C" standard reference projectile defined by the German steel, ammunition and armaments manufacturer Krupp in 1881.

This came from the wikipedia entry and there is a calculator here. Sure seems as if you need to shoot the bullet to get basic info needed for calculation (which is what my CRS riddled brain initially thought).

So the BC for my Lyman 457122 is .210 and my Lyman 457192 is .221.

[.45]

Check this out. A lot of info on BC and how it is figured. Not sure it will help you figure the BC for your bullet, but a lot of good info here.

http://www.hornady.com/ballistics/external.php

[w30wcf]

Check this out. A lot of info on BC and how it is figured. Not sure it will help you figure the BC for your bullet, but a lot of good info here.

http://www.hornady.com/ballistics/external.php

+1 Great tool!

Using the hornady ballistics calculator and the .45-75 data in the 1910 Winchester catalog - Muzzle vel - 1,383 f.p.s. 100 yard velocity - 1,108 f.p.s. the b.c. is .17.

Hobie,
The Lyman Cast Bullet Handbook shows a B.C. of .274 for their 457122 bullet, but based on the above your data looks closer to being correct.

w30wcf

[coyote nose]

Wow! Okay, so we have .170, .210, or .274! So far! I'll have to do some of the calculations myself since I am shooting 80%lino/20%lead and thus my bullet weight is way down.

[Hobie]

Wow! Okay, so we have .170, .210, or .274! So far! I'll have to do some of the calculations myself since I am shooting 80%lino/20%lead and thus my bullet weight is way down.

Yep, I based my calculations on my actual bullets all lubed up.

[flatnose]

BC, will change with velocity.

[Hobie]

BC, will change with velocity.

Yes that is mentioned in the linked information. In one example the C goes up and down all the way out to the target. I suppose you're really just "shooting" for an average so that you can do a mathematical guesstimate...

[coyote nose]

Check this out
http://www.handloads.com/calc/index.html
Using this for my Lyman 457122 solid (wt= 335, dia = .459, using 80%Lino/20%lead) I get a BC of .199
With wheelweights (358 and .458") BC= .214

[Old Savage]

Those shapes are usually around .2.