That depends on what powder I’m loading and what press I‘m loading on. With ball and some flake powders I check all of the first 5 and every tenth one after. Some powders like Unique, I don’t trust it so I check more often. When loading the countless thousands of rounds I have loaded on the XL 650 I only check about every 50th charge. That is only because I know what to expect from it. I know you asked about handgun but I have to say with extruded powder I check each charge. I’m not one of those guys that thinks a tenth of a grain will make a noticeable difference so I allow plus or minus a tenth.