It all depends on your ability and comfort zone with power tools...but I would seriously not recommend it!
While it is certainly possible for some folks to use power grinders / sanders and the like with decent results, for the rest of us who may not be as skilled, all it takes is one slip, oops or mis-calculation and bingo, you have ruined a perfectly good stock blank.
This happened to me about 25 years ago and then and there I vowed to only work on any future stock shaping projects with hand tools. In the time that has passed since then, I have never regretted that choice.
Yes, hand tools are decidely slower but...they eventually give you a far greater skill level in duplicating the subtle details which make longrifles / fowlers / etc the works of art that they are, better than any power tool can do. Hand tools give you the benefit of time to stop and take a critical look at what you have done, as well as the time to anticipate your next move.
Not only that, but the inevitable screw-ups that every gun builder experiences are much easier to fix.
Hand tools will (@ 90% of the time) give you a second chance to redeem yourself. With power tools, the odds drop like a rock to @ 10-20%.
Not very good odds IMHO...
Go buy yourself the rasps and files if you do not already have them. They cost considerably less than power tools do and trust me, you will become a much better craftsman and far more pleased with your end results!