can't google it. and i've seen only spent casings for 105mm guns during ROTC. what i'm talking about is whether or not ww2 guns and cannon cartridges had slim steel tubes brazed at the base, covering the flash hole from the primer pocket. the purpose is to transmit the primer flash deep into the propellant charge. igniting the charge near the middle, instead of at the base, is supposed to allow more complete burning and reduce chamber pressures significantly. that means you can gob more powder into a cartridge with little danger of exceeding prescribed pressure limits. in the case of the 105, there's a tube from the primer flash hole that extends barely an inch into the propellant charge. a gun writer, elmer keith, claims to have discovered the advantages of this with magnum hunting rifles. normally, slow-burning magnum charges take a lot of barrel length to burn (you can actually see particles of unburned powder exit the muzzle.) so he and a friend soldered a slim steel tubes into the casings so as to ignite the charge 1/3 up, instead of at the base. they submitted their findings to the US army, which couldn't adopt it into their field guns (so said keith,) but they were instructed to keep it secret, lest the germans use it to improve their 88s.