Humidity plays a big role in how a box call will sound on any given day. Have you tried to tune it at all by adjusting the screw on the lid? As mentioned before you nee to use oilless chalk, i use the half round pieces of blue chalk line chalk that you can buy at a hardware store. Also you should not do a lot of sanding on a box with sand paper use scotch pads that are less harmful as you don't want to remove wood from the call. Very little pressure is needed to get a good sound from a box all calls are different but for the most part just the weight of the lid will be all that you need. Just like shooting trad gear a box call will require practice to master to get the sound that you want. A slate is a good call but make sure you have a striker that will work in wet weather, some of the best days to hunt turkeys is in the rain. You can't beat a box call for locating long distance but once mastered they are a very effective close in call also, good luck.