The Split which penetrates the Head and Body of case is commonly known as a “K” Split. It is due to bad Cupping of the Brass (First stage process…Punch and cup from sheet.)
Will cause catastrophic case failure if fired ( with Possible rupture of Bolt and receiver walls as well.)
Low case splits are a sign of Bad Case Punch design (too tight a radius to form the inside of the Cup) and as a result, stresses are set up which will eventually form a crack ( Age or Season Cracking.)
Annealing the Head is not a solution, as the Head has to be hard anyway… Such splits are usually seen on “Folded Heads or Balloon head cases”, but in the right (?wrong?) conditions, can also show in solid Head cases.
Other reasons for the split are Bad sheet orientation when Milling, Impurities “streamed out” when Rolling the Brass, out of round drawing of the Cup, etc.
Kynoch had a problem in the Early 1950s with “Keyhole” blow-outs in .30/06 at the Web-Body junction…It was found that the internal radius of the Draw Punch was too tight, and actually “cut” into the case body inside…forming a stress Point, which then “Blew Out” on firing. ( 1952 or 1953 Lots…The Problem was rectified by enlarging the radius of the Draw Punch…)