The rifle has a lot to do with it as most of the ammo is loaded for the longer barrels and any carbine is going leave a lot of unburned powder that's going to "flash" when it exits the muzzle. Even the Finnish rifles will to a certain degree. An M91/30, and even better an M91, will produce the least flash with any ammo. As for which ammo has the least flash, I've never paid any attention to that. After all, I'm "all about the flash"!