I'm with Digs on this one. I aim to completely fill the grain on my stock guns with oil mixture alone. It takes about 30-40 daily coats, flatted off every 6 coats with very fine wet & dry, last 2 rub downs with fine pumice and then rottenstone. Not for the impatient!
If one does the flatting off thoroughly, you finish off with only a oil sheen on the wood surface but total in-fill of the grain.
This method will also fill in small dents and scratches.
The oil in the pores appears to unite with the oil that has soaked into the wood and bonds quite strongly. Problem with using grain fillers is that under some conditions they can literally lift out especially is tape of any sort is placed on the stock.
I remember seeing a Purdey that had been finished using grain filler. When sent off for the oval to be engraved, masking tape was placed round the oval to 'protect' the finish. When it was pealed off it took the grain fillings with it. Much profanity followed!
