I created this spreadsheet and tutorial a while ago: https://www.excelforum.com/tips-and-...thout-vba.html It is currently set up for 3 columns of 5 letters, but it should be easy enough to adapt to 4 columns of 10 letters:
1) Make another copy of column D
2) Edit start and stop values for each column
3) Edit and expand the text array that is currently in F2:J2.
4) Make enough copies of the bottom row to get all of the combinations desired.