I own over 30 box calls of all varieties, designs and woods. Here is my routine:
You'll need: Phillips screwdriver, 200 fine grit sand paper and some oil-free chalk.
LIGHTLY sand the tops of the rails in one long stroke end to end only 3-4 times. Your goal is to remove chalk and oil build up and residue to reopen the pores of the wood. You DO NOT want to change the shape of the rails or remove any wood. Repeat this procedure for the underside of the lid. You can get away with a little more sanding here as there is usually much more chalk and the lid is a little more forgiving than the rails. Again, do not overdue it. Lightly rechalk the lid with fresh chalk, DO NOT grind the chalk into the wood or chalk the rails, they do not need it.
For the tuning, I have found that due to normal wear, the screw usually needs to be loosened about 1/4 turn to regain optimum pitch. You may want to put a small pencil mark near the screw to mark the original position if much adjustment is needed. I like about 3/4 of the box stroke to be the high pitch note before it rolls over to the bottom note. The high note is what grabs the turkeys' attention and the rollover rasp finish note is what makes it sound authentic. If you close your eyes while playing the call, you can hear that the high note is easily buried by the louder rollover rasp if it is not longer in length. Never turn the screw in any direction more than 1/8 to 1/4 turn without trying the call again...it doesn't take much to change the angle of contact and therefore the pitch. Also try each side of the call after each adjustment, what does not suit one side may favor the other.
You did not elaborate on the condition of your box, but if the wood is chipped, dented or warped it may be damaged beyond repair. While a box is a simple design, the lid must ride precisely with constant contact over the rail for optimum performance.
Have fun and let us know how you do.
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