I'll give you a very simple answer.So guys how about an answer?? How thin is too thin? How do I tell when my grass has had it?
I'm sure I can read the lit on the casemaster but would appreciate your thoughts.
No matter how many loads have been put through your brass, once you get to the fifth trimming, they are at the end of their usefull life.
As stated elsewhere, the brass is thinning in the critical head/case wall juncture, and a thinning groove may or may not be present.
Think of it like this. If you trim .010" off the neck each time, and you get to the fifth trimming, that's .040" of brass that has migrated into the neck and has been removed.
All brass is not equal in the amount it has at the head/case wall juncture, it varies from each manufacturer. So to be safe this is a 'rule of thumb' put out by brass manufacturers, some brass may go longer than this before it pulls in two, but do you want to run the risk?