That is so overkill, just use a modified greenhill formula and you'll literally get the same numbers that kolbe formula provides, with 1/10th of the input required...all you need it bullet diameter, and bullet length, and use a C between 100 and 133 (for subsonics, I actually use a custom formula to determine C but really anything between 100 and 133 should suffice for airguns shooting around 1000 fps...)..
100*Bullet Diameter^2/Bullet Length