European cartridges have to be proof tested also (random samples from a batch) to see that they fall within safe limits compatable with the pressures for which the gun was proofed. Such ammo boxes will be marked with the CIP logo. Certainly the older American made Winchester AA cartridges imported to Britain and the Remington RXP's in the 1970's were found to be well over the safe limits for 2 3/4" chambered English guns. American ammo is quite punchy; or at least was then. Even if you have an English 2 3/4" chambered gun I would be cautious about using non-CIP ammunition. Lagopus.....