When you fire a centerfire cartridge, several things happen, in order.
The primer pops, shooting a jet of flame though the flash hole. The flame ignites the powder. The powder burns, producing high pressure gases. The gases are pushed by through the flash hole, their pressure being increased by the venturi effect of the small hole, and push the primer back. The case walls of the cartridge expand until they hit the chamber wall. The cartridge case is slammed back against the boltface/recoil shield, reseating the primer. Finally, when everything else that can possibly move has moved, the gas pressure overcomes the bullet's inertia, and starts it on its trip down the barrel.
If you shoot a blank, the same thing happens, up to a point. The gases back out the primer, but without a bullet blocking the front, the case does not get slammed back, and the primer does not reseat.
In a rifle or an automatic pistol, this is of no concern. With a revolver, though, the backed out primer can prevent the cylinder from moving, either to turn or to come out of the frame for reloading.
The solution, I've always heard, is to drill out the flash hole. If you increase the flash hole size, until there is just enough bottom of the primer pocket left to hold the primer, that gets rid of the venturi effect, and the gas pressure is not high enough to back out the primer. Okay. That makes sense.
Then I hear, "alway mark the case, like with a file-notch on the rim, so that you do not accidentally use these cases for live rounds. This is very dangerous". I always accepted that as true.
A few years ago, Winchester came out with some new ammo, designed for indoor ranges. They called this stuff, "Non-Toxic", and it did not use lead in the primer. This new primer was, apparently, not as hot, because Winchester made the cases with a huge flash hole (45 ACP, standard Large Pistol primer pocket size). I ended up with a couple hundred of these, and wrote Winchester, asking if these were "one-shot disposables", or if they were reloadable, and if so, what load data. They wrote back saying they were perfectly safe with any normal load data.
So, now (FINALLY
) my question. If the WW with the huge flash hole are safe for reloading, why are the blank cases, with the huge flash holes dangerous? Are they really dangerous, or is this an old wives' tale (like deactivating primers with oil) that has been around for donkey's years, and every body "knows" it and repeats it, but there is no hard data to back it up?