Many times I have said something was wrong with our American .303 Britishicon cases now even the European CIP seems to agree.
("practical incompatibility with ammunition made for the corresponding chambering")

Delta L problem
The delta L problem (ΔL problem) is a condition that occurs regarding certain firearms chambers and their practical incompatibility with ammunition made for the corresponding chambering. The ΔL refers to a Commission Internationale Permanente (C.I.P.) geometric dimensioning and tolerancing definition for firearms cartridge cases which are longer than the chamber they have to fit in.

Conflicting industry standards
The main cause for the ΔL is that the two main civilian ammunition and firearms industry standards organizations C.I.P. and SAAMI have assigned different standards for the same cartridges. This leads to officially sanctioned conflicting differences between European and American ammunition dimensions and chamber dimensions. Since C.I.P. and SAAMI do not rule nor control civilian ammunition standards worldwide other causes for conflicting standards leading to ΔL issues are also possible.

Firearm cartridges with otherwise problematic headspace
There are also some firearm calibers with problematic headspace listed by C.I.P.[2]
The headspace defined by:
Depth of rim recess
.303 British
.38 Sp AMU
6.35 Browning
7.65 Browning
9 mm Browning long

Delta L problem - Wikipedia, the free encyclopedia
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