Without the lube how would the neck be effected ? I can't see how that little bit of rearward movement would effect the neck diameter, unless I'm missing something, I can't see it. I see neck diameter springing back after the bullet is fired. A loose military chamber can explain that, soring back that is, but not a factory rifle
What I do not want is this:
or this
or this
These case head separations occur under the following conditions: a dry case is fired in a dry chamber, and the base to shoulder length is less than chamber headspace. That is, there is clearance between the case and chamber. When there is a gap between bolt face and cartridge face, because the dry case neck is fixed to the front of the chamber, something has to give when pressures climb. And what gives is the sidewall of the case. The sidewall stretches.
You can see the stretch develop in Varmit Al's finite element models.
Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning FEA Calculations done with LS-DYNA
it is particularly bad in semi autos. These guns are designed to unlock when there is still some residual pressure in the chamber, that low pressure, less than 650 psia, helps pop the case out of the chamber (called the residual blowback effect) and increases the time there is energy to move the mechanism. It was common advice to fire a cartridge in a Garand or M1a no more than five times, or the reloader would experience case head separations. Sidewall stretch and case head separations can be reduced to almost nothing by lubricating cases fired in Garands and M1a's. This is my experiement, I took one set of LC cases 22 firings without any evidence of sidewall stretch, in a match M1a
I shot Master class and High Master scores with these rounds, so accuracy was excellent. I used paste wax on the cases because paste wax dries hard and does not attract dirt, like grease does. Paste wax is a combination of several waxes, but one of them is the same stuff that Pedersen applied to his cases.
what caused the loss of these cases were case neck cracks and body splits
I could have reduced the number of case neck cracks by annealing, but when you are shooting in NRA competition every weekend possible, at least three times a month, case neck annealing takes too much time. At least then, expensive rotary case neck annealing machines were not on the market. And also, my ammunition would mostly hold the X ring at all distances, which is good enough accuracy to win the National Matches. Winning the National Matches takes more than just good ammunition and a rifle, but if the combination will hold half the ten ring, then not winning is not the fault of the rifle and the ammunition.
Lee Land is a Civilian Service Rifle Champion, winner of the President's 100, F class and bench rest shooters would consider his reloading process primitive and barbarous. I was squadded with the guy, his ammunition would chamber, go bang, and extract. And with a properly thrown powder charge, in a case that was hand trimmed with a file, full length sized in a standard sizing die, with a good bullet and the cheapest primers around, he would clean the target.