Originally Posted by matt g
Odd, it would appear that only lead free ammo has the small primers. Could it just be due to a lighter bullet and therefore a lighter powder charge?
Probably not. The smaller flash hole found in cases using the small pistol or rifle primer has been shown to produce a hotter more intense "flame" in many cases than the larger primer and larger flash hole.
Obviously the smaller primers don't have the quantity of "primer mixture", but by concentrating the burning mixture through the small flash hole apparently produces a more consistent ignition of the powder charge.
This is also true of several rifle cases such as the 6mm and 22 PPC cartridge that was developed from the 7.62X39 round that originally used a large rifle primer, but at some point during the development of the PPC, this was changed to a small rifle primer and smaller flash hole which was shown to produce superior accuracy.