Saeco #640 ballistic coefficient

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steveu834
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Saeco #640 ballistic coefficient

Post by steveu834 » Fri Mar 26, 2021 2:50 pm

All,
As the subject line says, does anyone know what the Bc is for the #640 bullet. I am going to shoot my 40-50 SBN past 200 yards and would like to have some idea of what my elevation changes would be for BPCR.

Cheers,
Steve

bruce m
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Re: Saeco #640 ballistic coefficient

Post by bruce m » Fri Mar 26, 2021 3:37 pm

not sure exactly, but it might be 0.4 or a little less.
if you know your muzzle velocity and sight radius, you can refine that by shooting and using the numbers on the j b m ballistics website to get a true b.c.
bruce.
ventum est amicus meus

gunlaker
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Re: Saeco #640 ballistic coefficient

Post by gunlaker » Fri Mar 26, 2021 4:07 pm

I use 0.4 for a BC with the Saeco #740. It predicts the trajectory well to 600 yards. The Saeco #640 is lighter so will have a somewhat worse BC.

Chris.

John Bly
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Re: Saeco #640 ballistic coefficient

Post by John Bly » Fri Mar 26, 2021 6:43 pm

I shot the 640 on pigs last week at 300 meters. I had to come up about 4 minutes but it was 28 deg when I shot and I've always had to come up when it is cold outside. So it may not be much different. I missed one but it was my fault.
"Perfection consists not so much in doing extraordinary things as in doing ordinary things extraordinarily well"

bruce m
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Re: Saeco #640 ballistic coefficient

Post by bruce m » Fri Mar 26, 2021 9:52 pm

4 minutes compared to what?
bruce.
ventum est amicus meus

John Bly
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Re: Saeco #640 ballistic coefficient

Post by John Bly » Sat Mar 27, 2021 6:13 am

I would have normally shot a Brooks Creedmoor style at 416 grains. I used 2 grains less powder because the 640 set deeper into the case than the Brooks.
With the lower weight of the 640 I figure the velocity was about the same, but I did not chrono it. I just wanted to try the 640 on pigs and I was satisfied with the results on the first time out. I was shooting a 40/50 Sharps Straight on a Shiloh '77.
"Perfection consists not so much in doing extraordinary things as in doing ordinary things extraordinarily well"

John Boy
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Re: Saeco #640 ballistic coefficient

Post by John Boy » Sat Mar 27, 2021 7:08 am

Steve, you can calculate the BC of a bullet using this calculator ... https://tmtpages.com/calcbc/calcbc.htm.
Regards
John

art ruggiero
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Re: Saeco #640 ballistic coefficient

Post by art ruggiero » Sat Mar 27, 2021 10:43 am

with my 40/50 ss the up is 13 to 14 min from 200 to 300 yds 32 in. barrel art

MikeT
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Re: Saeco #640 ballistic coefficient

Post by MikeT » Sat Mar 27, 2021 12:52 pm

steve,
If you have some one available to you that shoots a 40 caliber BP rifle, use their come-up from 200 yards. You will be very close using their come-ups for any distance they have sight sittings for.

Keep on hav'n fun!
MikeT

bruce m
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Location: australia

Re: Saeco #640 ballistic coefficient

Post by bruce m » Sat Mar 27, 2021 5:05 pm

John Boy wrote:
Sat Mar 27, 2021 7:08 am
Steve, you can calculate the BC of a bullet using this calculator ... https://tmtpages.com/calcbc/calcbc.htm.
i have tried this method, and j b m has a similar one.
not knocking it, but have never got a number that matches shooting results.
it is quite complicated to get all the correct inputs due to variables almost beyond control.
using known muzzle velocities and comeups for a number of ranges in true moa and typing various b.c.s into a good trajectory calculator until you get one that matches has proven to be simpler, better, and more accurate.
bruce.
ventum est amicus meus

beltfed
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Re: Saeco #640 ballistic coefficient

Post by beltfed » Tue Mar 30, 2021 9:13 pm

Steve,
FWIW,
The Lyman Cast Bullet Handbook, #4
lists the Saeco #640 at a B.C. of 0.324
Hope this helps.
Also, my own 40-65 come ups from 200 to 300 to 400 to 500yds are about 11 minutes each
with my load of 370 gr E-minigroove bullet clocking 1375fps
You should be able to get close on target with the 640 by about 12 minutes each 100yds increase
from 200 to 600yds.
beltfed/arnie

steveu834
Posts: 7
Joined: Wed Mar 25, 2020 12:42 pm

Re: Saeco #640 ballistic coefficient

Post by steveu834 » Mon Apr 05, 2021 1:41 pm

All,

Went to the range on friday, it was quite windy but manageable. The BC for the 640 seems to be .350 @ 1260 fps. I had a low shot in the rear foot and the ram fell over, other shots in the body knocked them over also. The only shot that failed to take the ram was a half bullet strike in the belly. Shot 50 rounds with a blow tube and the bore was wiped clean with 2 patches. Still going to look for a 740 mould to test.

Cheers,
Steve

steveu834
Posts: 7
Joined: Wed Mar 25, 2020 12:42 pm

Re: Saeco #640 ballistic coefficient

Post by steveu834 » Mon Apr 05, 2021 1:44 pm

beltfed wrote:
Tue Mar 30, 2021 9:13 pm
Steve,
FWIW,
The Lyman Cast Bullet Handbook, #4
lists the Saeco #640 at a B.C. of 0.324
Hope this helps.
Also, my own 40-65 come ups from 200 to 300 to 400 to 500yds are about 11 minutes each
with my load of 370 gr E-minigroove bullet clocking 1375fps
You should be able to get close on target with the 640 by about 12 minutes each 100yds increase
from 200 to 600yds.
beltfed/arnie
Thanks for the info. I am going to have to do more testing with some lubes and try to bump the speed up a bit.

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