I cannot find small or large pistols primers anywhere. Out of "desperation", I bought small and large pistol primers for reloading my 9mm, .40 and .45 caliber bullets. The guy from the store said it was safe to use but just to back down on the powder. Presently I am using WInchester WST 5.0 gr for the 9mm. Generally, how much of powder should I decrease using these magnum primers? I am not looking for match grade accuracy. These bulletrs are used for plinking. Thanks THR.