Shiloh Rifle Forums

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

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.

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.

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.

4 minutes compared to what?
bruce.

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.

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

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

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

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.

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

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

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.

Update: I shot the 640 on Sunday from 200m to 500m and after correcting for my sight radius the bc of .324 works for my load at 1200fps. I got 9 of 10 rams, I shot over one.

Thanks for the help,
Steve