Calculating a cast bullet BC?

[TedH]

I know I saw a program before to calulate a cast bullet's BC from it's dimensions. I had my ballistic calculator all set up in my smart phone, but then that phone met an untimely end. I'm trying to get my 45-70 data set up in the new phone, but can't find the BC for a particular bullet, namely the Saeco 45 caliber 480 gr. bullet, the 645 Mold. Appreciate any help on finding the BC for that bullet.

[Norbrat]

http://tmtpages.com/calcbc/calcbc.htm

[Von Gruff]

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

[rsterne]

The best I have found because it is the most flexible and will accept almost any bullet shape and gives the output at various velocities.... This is important as the BC is FAR from a constant, particularly if the bullet is subsonic at all....

http://www.border-barrels.com/drag.htm

Bob

[Tom Myers]

I know I saw a program before to calulate a cast bullet's BC from it's dimensions. I had my ballistic calculator all set up in my smart phone, but then that phone met an untimely end. I'm trying to get my 45-70 data set up in the new phone, but can't find the BC for a particular bullet, namely the Saeco 45 caliber 480 gr. bullet, the 645 Mold. Appreciate any help on finding the BC for that bullet.

Using this estimated BC calculated a trajectory that was quite close to actual firing.

[TedH]

Thank you Tom. That's not the exact bullet, I'm using the 645 mold, but it should get me pretty close. An extra 110 grains of weight might change it more than I think though. First chance I get I'm going to set up my crony at 100 yards to get an exact BC.

[rsterne]

Ballistics Coefficeint is proportional to Sectional Density (ie weight), so adding weight with the same shape will increase BC....

Bob

[Tom Myers]

Thank you Tom. That's not the exact bullet, I'm using the 645 mold, but it should get me pretty close. An extra 110 grains of weight might change it more than I think though. First chance I get I'm going to set up my crony at 100 yards to get an exact BC.

If the shape is the same, an increase of 5 grains would raise the estimated B.C. from 0.3062 to 0.3104.

When you do get a chance to get an exact B.C. for that bullet, please post the results here. It is always interesting to compare estimated values with real world values.

[TedH]

Yes, the shape is the same, it looks identicle to your pic. Do you think that increase would be proportional up to 110 gr. increase? That seems like it would be pretty high. That would put my BC over .400.

[Idaho Mule]

Could this possibly become a sticky?? Some very good information. JW

[Tom Myers]

Yes, the shape is the same, it looks identicle to your pic. Do you think that increase would be proportional up to 110 gr. increase? That seems like it would be pretty high. That would put my BC over .400.

If your nose shape is exactly the same (Same tip width and Ogive Radius) and you increase the length of the body so that the weight would be 481 grains (That would be one looong 40 caliber bullet) The BC would have a calculated increase to 0.3971 (0.3063 / 371gr x 481gr).

The Saeco 740 has a nose shape similar (but not quite) and weighs 405 grains so, if the nose shapes were exactly the same, the anticipated B.C. increase would be 0.3323. (0.3065 / 371gr x 405gr)

However, here is what the 740 actually has for a nose shape. It has a smaller Ogive radius so the B.C. increase is only up to 0.325

Observe the values of the Form Factor down in the right corner of the sketches.
That form factor is derived from Ogive radius, Tip diameter and,in the case of Cast bullets, bullet length.

[TedH]

The 645 Saeco is a 45 caliber.

[Tom Myers]

The 645 Saeco is a 45 caliber.

Yep, that one slid right by me. Oh well, the concept is the same when applied to bullets of the same caliber.