I used to have a local firearm restoration business. I did a lot of stock work as well as hot salts bluing. I'd use ordinary, full strength strippers like Zip Strip and Kleen Strip etc. Often times it would take three or four applications to remove all of the original finish.
My technique was to apply the chemical with a disposable paint brush and allow it plenty of time to work, at least 20 minutes or so.
When the finish began to bubble up, I'd scrub the chemical and the loosened finish off of the walnut under running COLD water and repeat as many times as necessary. I learned the hard way not to use hot water because it caused a reaction with the chemical which would generate visible fumes which distorted the air almost like a mirage does. These fumes are toxic and rather overpowering.
I'd use a soft brass bristle brush to clean out checkered areas as well as other little "tight spots". When finished, I'd allow the wood to air dry in a dry environment. Near a woodstove is ideal. Not so close as to heat the wood, but in the vicinity in order to ensure that the wood dried thoroughly. From there, some fine (220 grit) wet or dry paper was usually all that was needed to cut back the grain which of course would raise significantly after being soaked under running water several times. From there, some final sanding with progressively lighter grits usually up to 400 grit and then whatever finish you decide upon can begin.