One thing what is needed to supply your own (or Lapua's or ...) drag function to BfX is a function called BfX_CRC. CRC means cyclic redundancy check. It basically computes a 13 character text from a range of cells - no matter how large. If anything changes - the number in the text changes. It will be used to tell BfX that a certain drag table does not have to be read again because nothing has changed.
This was a small project gone out of hand. It completely generalized the internal structure of BfX (for the better) and the implementation process discovered a few bugs you probably never encountered. I updated the Getting Started workbook- you realy have to have a look at the "check range changed" worksheet to see the raw power of BfX CRC in spotting the smallest change in this rather huge workbook.
BfX_CRC noticed that under windows XP and Excel 2003 BfX_CD didn't work (why did no user of BfX report this to me?) and spotted a few deviations in the worksheet that contained the BfX_Ran functions. These turned out to be a worksheet problem that I fixed. Now there is an single issue left with no practical impact - BfX_CRC spots a deviation in the cell G500 of the Drag Functions worksheet between Excel 2003 Windows XP and 2010, windows 7 64 bit . However, the number therein is to the last if its many decimals, the same! I will have a digital debug look at it later.
The updates can be downloaded from the site.
I will download and update BfX and have a read of whats changed.
... soon I'll will post another update - the one in which you can supply your own, Lapua's or other drag functions.