rimshot
You are starting out in a pretty big hole... while the yellow birch typically used for the model 70 stocks is fairly high quality wood to start, it is possible you have a soft example or a different species which is tough stuff to deal with.
I am making a couple assumptions to arrive at that, namely you appear to want a dark stock and an oil finish. I am guessing the color did not please because it turned a muddy color, likely with green tones that look real bad in good light? It is not an uncommon and thing why most folks would suggest that you test any finish on an inconspicuous piece... like the barrel channel....
Test for hardness by pushing a thumbnail into a raw spot in the wood. A big mark would make you want to question saving the stock...
Any chemical stripper should work fine, but the water-flushed ones are probably best avoided. Zip-strip is one I have used as well as the Formby's "refinisher" which is just solvents and would have gotten you where you wanted to be before the additions. I would try the Zip-Strip first now.
After you get the finish off as much as possible and the stain starts being difficult, get a set of Daly's Wood Bleach. It is a two-part system that uses fairly strong Hydrogen Peroxide as one part and sodium hydroxide (lye) as the other. They can be used mixed, one and then the other or either alone.
In general, both pre-mixed has worked best for me. DO not try to flood the wood, just brush some on with the cheap synthetic brushes you can buy at most hardware stores. I usually rinse with a very dilute solution of vinegar and water after, but it probably is not really needed.
Attacking the stain with the Zip-Strip and then the bleach and repeating each will probably be required. The bleach will have little effect on the finish, it is the paint stripper that will do most of the work, aided by you...
Do not sand anything until you get the finish and color out and let the stock dry very thoroughly... If you get this far, lightly sand with 400 grit or finer paper before applying a sealer coat of oil, before putting on the new (and tested) coloring agent. By sealing first, the wood absorption will be reduced and make you apply the color in light lifts, rather than a single thick layer.
If I have misguessed where you are, or what you are trying to do, please let me know and I will see what I can do...
art
