BC should be about 0.229 to 0.267 based on other flat points, with a very wide one like is on the Hornady 300 grain .375 bullet getting the lower number and the and less wide FP, like the Sierra 200 grain .375 bullet shape, getting the higher number.
Sectioning, I drill a slightly oversize hole in the end of an adequate length of scrap 2×4 and use hot-melt glue to glue the bullet (or case) into the hole. When it has set, I use a bandsaw to section it, leaving just a little extra material. After sectioning, I use wet/dry paper spray-glued onto a piece of scrap plate glass or other flat surface to remove the saw blade marks. You may need to go down through a couple of grits to get the finish you want. After all that, I pop the bullet or case half out of the wood and peel the hot-melt off.
Sectioning, I drill a slightly oversize hole in the end of an adequate length of scrap 2×4 and use hot-melt glue to glue the bullet (or case) into the hole. When it has set, I use a bandsaw to section it, leaving just a little extra material. After sectioning, I use wet/dry paper spray-glued onto a piece of scrap plate glass or other flat surface to remove the saw blade marks. You may need to go down through a couple of grits to get the finish you want. After all that, I pop the bullet or case half out of the wood and peel the hot-melt off.