So, you appear to have a Czech large-ring Mauser action there, made by CZ, but beyond that those markings are useless.
The original chambering would most likely have been 7.92 (aka 8mm) Mauser, but it could be anything now. If it has been rechambered or rebarrelled, the marking SHOULD be somewhere on the barrel. Try removing the stock and looking at the underside of the barrel.
There is a significant difference between .270 and .243 cases, with the .270 being much longer for one thing. It should not be possible to accidentally chamber a .270 cartridge in a .243 barrel, but may be possible to chamber a .243 in a .270.
You cannot rule out that it may be some other chambering entirely either.....
If you cannot locate a marking on the underside of the barrel, a qualified gunsmith should take a chamber casting to be sure.
Good luck!