This picture shows quite graphically, why I keep spouting off about making your brass fit the chamber if you want your brass to last.

Note the case on the left - it has the longest neck length. This means the body of that case is the shortest of the three and if that case is shot in a longer chamber, the body will blow forward stretching the case - usually at the web - causing premature case loss in a loading or two, ending in case head separations at the web - unfortunately normal for the .303 due ot sloppy chambers and failure to fit brass prior to it's being fired the first time.

The case in the middle has a slightly shorter neck than the left case, and appears in the middle of the two outside cases for neck and body length. Note the different shoulder of the far right case - having a slightly shorter neck and the shortest body length as well, due to it's sloping shoulder angle.

Brithunter - as you noted - the chamber walls are not sloppy like many military chambers show. They fit the ctg. base nicely and should promote longer than normal case life.