I had the opportunity to cherry pick a bunch of “scrap” gun part sized pieces of tool steel lately. Alot of it is typical A-2 but there is also some S-7 and D-2 and another marker M-4 as well as V-23. I have machined a lot of S-7, D-2 and A-2 but only blued A-2 and maybe S-7. Not familiar with V-23 or M-4 and there are a lot of square bridge sized pieces of both. Does anyone have experience with bluing these two steels?

Couldn't find anything about a steel specification of "V23", are you sure that it's specification?
M4 is one of the high Molybdenum/Chromium tool steels that may not blue at all in a normal bluing process; makes good drill bits or other high speed cutting tools but doesn't machine very well itself.

All of the above will blue....but will not color match to other "gun" steels.