Phil3
I have a 30-30 that I have had for over 30 years, the 30-30 is rated for a max chamber pressure of 38,000 cup or 42,000 psi and the primer always protrudes from the rear of the cases. I alway full length resize these cases with the die making hard contact with the shell holder or press cam over and many of these cases I'm reloading are as old as the rife.
P.O. Ackley did an experiment with a 30-30 improved testing bolt thrust in a Winchester 30-30 and removed the locking lug, the cartridge was fired, the case did not stretch or move and the primer only protruded slightly more than normal.
Bottom line, a case will stretch when the chamber pressure reaches the yield strength of the brass, and it will stretch until the rear of the case contacts the bolt face.
On the majority of rifles when fired, the firing pin hits the rear of the case and drives it forward until the shoulder of the case contacts the shoulder of the chamber. This action creates your head clearance or the air space between the rear of the case and the bolt face, this air space causes the case to stretch when the chamber pressure is high enough to cause the brass to stretch.
Many military rifles have extractors designed to prevent the case from moving forward until the case contacts the shoulder of the chamber and this adds a safety margin for cases made on the short side and helps prevent case head separations.
Shoot your short .223 cases and buy a RCBS Case Mastering Gauge and you will never have a case head separation, in over 40 years of reloading I have never had a case failure other than split necks.
If you really want to worry about headspace and head clearance then just buy a British .303 Enfield, when the bolt closes the extractor moves away from the rim and leaves the case unsupported.
Yes I know its a rimed case but look where Remington put the shoulder of the .303 British case.
Below shows you the actual location of the fired shoulder and how far you would push the shoulder of the case back with a full length resizing die. The case pictured was completely full length resized and the case started to separate on the 3rd firing. Therefore your short .223 cases are minor and only require firing at a lower chamber pressure to blow out the shoulder to the correct length.
phil3 at maximum military headspace the Enfield rifle can have .017 head clearance and emergency wartime headspace was .10 more than that, and phil3 you just have a "small minor" problem that can be fixed.
The cases below were full length resized with the die making hard contact with the shell holder or cam over and fired in a new Savage .308 until they failed. No attempt was made for minimum shoulder bump and the dies were adjusted as per the manufactures instructions.
NOTE: Chrome chambers or plated cartridge cases will have "less" case stretch when fired, when I fired my short .223 cases in my mid-length carbine with a chrome chamber at higher chamber pressures than stated above I still did not have any case stretching.
In a Enfield forum a British member got tired of us "Americans" talking about headspace and said to us "Oh just shoot the bloody thing".
I have one lapped shell holder thats .003 shorter than normal and two sets of shell holders that are .002, .004, .006 .008 and .010 taller than normal. I also have a Lee shell holder for a .223 that was manufactured by them .005 shorter than normal, it has a manilla tag with the string tied through the center hole and the tag is marked "NFG" and it is now in my junk box. 
don't tell Phil3 I grew up in Milpitas next door to him when Ike was president and the silicone valley wasn't invented yet. (old Republicans are tight with their money)
