Chapuisarmes , buddy I have the same stock all I used as a filler was some rotten stone powder mixed CCL stock oil until filled rubbing in with a 2"x2" of soft cotton then wipe off and hand rubwith your palm
leave it for 2days loner the better then applied ballistol , the world's best oil IMO wipe down and keep applying ballistol I am happy with end finish for field use. I buy the ballistol in the neat oil form not the spray .... hope this helps.

ps rotten stone is bloody hard to find !!