Kestak, Before Internet Reloading there was Reloading, Back THEN there was a company that made flash hole gages, like RCBS says when offering Competition Dies and Gold Medal dies – Competition dies are not for everyone.
As you can see when you read through the responses, the diameter of the flash hole is not a concern of everyone. I suggest purchasing set of drill indexes of numbers and letters, good ones cost $100.00 +, for flash holes a set that starts at .100 maximum diameter would work for flash holes, you could use the shank end of the drill bit as a transfer to determine the diameter.
Those that drill all the flash holes suspect there is nothing to be gained, but it is a JIC thing – JUST IN CASE. Others? As in those that purchased the flash hole gages, and those that have shell holders for different purposes measured flash holes, again, if the reloader before Internet Reloading did not measure before firing and again after firing the money spent on the flash hole gage could have been spent on other tools.
I purchased 22,000 cases, mostly pistol, I started sorting when I came across a few I did not recognize, when looking for a difference I found the flash hole gage did not touch the wall of the flash hole and the cases had small pistol primers, for me it was too much trouble to sort by primer size, so, I offered them to a commercial reloader friend. He was not interested, the added time and cost and change time for him to reload 45 ACP ammo with large and small pistol primers meant he had to sort 45 ACP and load in two different stages. Does not seem like a problem but he purchased by the pound, the seller did not separate, this forced him to separate and then sell, by the pound, the small primed NT cases.
F. Guffey