This article explains what happens with military discounts at Best Buy.
Does Best Buy offer military discounts?
The Best Buy military discount is only available on a case-by-case basis at participating retail locations. There is no actual military corporate discount program.
If you want a discount, you must go to the store and ask to speak to a manager. The manager will then decide whether you will get a discount on the items you buy.
Due to this process there is no standard discount. You can not be sure that you will get any discount at all; it is strictly up to your local store manager.