CAS mark on No4

Can someone shed some light on what the CAS mark on a No4 7.62 conversion means please

It is the proof stamp that the rifle passed when it was rebarreled to 7.62 or commonly called at the time the crack test stamp. At Lithgow.

I've seen both CAS and CAL stamps; I'm certain that the CAL one is Lithgow, and have read somewhere that Sportco in South Australia did the crack testing as well, which might explain the different mark.