The least harmful chemical I have found is also one of the cheapest: rubbing alcohol. I highly recommend it for the wooden components of your firearm. A little alcohol, Q-tips, paper towels, elbow grease, and patience will reward you with a clean, DRY, wood stock, ready to stain/tung oil.
With all due respect, I cannot recommend pouring boiling water over the entire firearm.
Harsher chemicals can be used on the metal components than on the wood, IMHO. Water will just delay the final prep of your stock. In my experience, the average wood stock takes about 3 hrs a day of work, including initial cleaning, steaming-out of dents, repair, etc. The rest of the day is allowing the stock to breathe and reduce its content of moisture. Once cleaned, repaired and stained, apply tung oil in thin coats over the entire surface of the stock, esp. to the INSIDE, using 0000 steel wool in between applications. Patience will be rewarded. Figure on 7 days for a service-grade job.