Stock count differences classification

Hello.
I wonder if anyone can help me on the below:
in a manufacturing company is it correct to classify stock count differences of raw materials as usage variances? Or should normally be classified as inventory differences? In addition if these are classified as usage variances does this classification affects Gross Profit on the contrary to the other one that goes under gross profit?
Is there any specific guidance in which the above is clarified?
I would appreciate your help