The BC is something between .105 and .159.
Take your dope and try first 0.124 to 0.140.
With longer ranges you will see a big difference between temperatures.
I have quite good data (it seems) as I spent 2 days at the range, on 1st day 300m showed 18.4mil (zero at 0.9mil) and on second day it showed 17.8mil.
I pondered at first if I could trust it but the shot was right on.
On to the matter...
You have set on your cartridge. Then you should collect dope for the cartridge, from your gun.
At the range wait for ammo to warm/cool to ambient temp. Avoid sun ofc. You can shoot, but do not take markings until 5-15 minutes.
Shoot at 25m (I recommend zero there too. You can set the zero at home so you do not waste range time)
Then continue all the way as small steps at a time as the range allows.
Note the dope results (elevation) and windage (Held or dialed) on the paper along with all weather information on the top.
Then input the correct drops to DSF readings to correct the flight path. Because of this the original BC does not matter very much.
If you have chrono, take velocity markings from 20-30 shots. Discount possible errors/cartridges with bad loads so they do not ruin average.
If not, pick the manufacturers MV if the ambient is near 20C (70F).
Take the Kestrel and in the gun->MV go to enable MV table. Add this chrono or SWAG MV there. ---I should note that giving guessed data to MV table is very risky but it could have huge benefits.---
Then the next time you are at the range with different ambient temp, shoot and collect data again. Then go to Cal MV in the Kestrel and add the drop. It will add the new number to the MV table and can from that data (2 datapoints) extrapolate any temperature!
After this you have robust data and enabled all Kestrel functions.
-Dope chart
-Dope in Kestrel
-DSF set in Kestrel
-MV table set in Kestrel