[Bart B.]

Again, I have fired 8mm57 ammo in an 8mm/06 chamber, .121” longer chamber, meaning the shoulder of the 8mm57 was .121 + from the shoulder of the 8mm06 chamber, cases after firing were ejected as 8mm06 cases with very short necks, the firing pin did not drive the case forwarded, the case did not remain the same length, the case got shorter.

Fact or fiction, truth or nonsense. The M1917 has an exception.

Same thing happens shooting a .308 Win. round in a .30-06 chamber. And there are other mismatches that'll do the same. Such is very normal when the extractor's holding the case head near the bolt face while the primer's struck by the firing pin. Nothing new about this at all.