If the guy running the lathe uses a standard go gauge to headspace an Ackley chamber, the case will stretch too much in fire forming and get frequent case separations just behind the shoulder. This problem is common as dirt.
I have tried ~~ 100 fixes and the best I have found is 10 gr of any pistol powder [that would be 5 gr for .223] covered with cream of wheat and fired without a bullet. The case is slathered with a film high pressure lubrication like moly grease. This forms half a shoulder and does not stretch the case too much behind the shoulder. That half shoulder can stand up to the push of the firing pin. That is unlike the base of the case neck cannot stand up to the sharp shoulder neck base and there will be a ring of plastic deformation. Ackley chambers should be headspaced so new brass crushes .004" [on bolt closing] at the base of the neck. The case then does not move forward on fire forming with the tighter headspace.
The half formed shoulder can be full power with bullets with full accuracy. There will then be a full shoulder for the 3rd firing.
There are other good fixes. A mandrel can open up the case neck that can then be partially full length resized so that there is .004" of crush on bolt closing. Or the barrel can be set back .004".
