Do a little searching folks and there's any number of somewhat mutually contradictory stories out there.
The drive for less lead on pistol ranges includes changes in the primers. The idea is to balance the weaker flash from a less toxic primer with a larger flash hole for substantially similar ignition. See also the move to small primers. See also Bill Jordan's discussion of enlarging flash holes for wax bullets then segregating the cases compared with the current general experience that larger and common size flash holes don't matter much for normal use on a square range. CF with the NT marked cases and small primers.
From a Tom C
I found two distinct different flash holes (0.081 and 0.098 with gage pins) with about 60% of the smaller size. I wrote Federal and their answer was there should be no difference (gee thanks).
I went to the range today and shot three 25 shot strings.....You can see the velocities are almost identical with the Nosler Reloading Guide #4. You can also see from the data that the case weight and the size of the primer hole did not seem to matter
Now gone from the website with the move to small pistol primers Winchester once said:
Regarding the enlarged flash hole of the shellcase loaded in 45 Auto WinClean products (WC451 and WC452): The flash hole in this shellcase was enlarged in order to achieve optimal ignition while utilizing a lead/ heavy metal free primer. Winchester conducted extensive testing prior to the introduction of this product and determined that the larger flash hole will not have an adverse effect on reloads using standard leaded primers. Please remember, Winchester does not offer a component lead/ heavy metal free primer. Other calibers within the WinClean line are manufactured with a standard diameter flash hole. As always, reloaders should utilize published data from a recognized source and work loads up carefully.
Others say the Federal at least will have loose primer pockets sooner than the conventional size flash holes. Some worry about powder sifting back into the primer or otherwise having more leaking primers and breechface erosion. Some say the Speer Gold Dot as optimized for short barrels uses a slightly enlarged flash hole.
On the other hand the PPC folks demonstrated pretty conclusively that ignition matters and varies with primer flash hole size as with primer size. See also Jim Carmichael's efforts with small rifle primers in the .308 case head and so it goes.
