The brass casing was never part of the 152’s basic issue in either the Sheridan or your M60 Starship after early deployment in Vietnam, which is why the Sheridans burned like they did.
As you probably know, the whole 152mm system concept ended up being regarded as a failure and all the active duty M60A2s were taken out of service by 1981. They were either re-turreted with a conventional gun as the M60A3 or converted to bridging vehicles without a turret.
Thanks for the end of ‘brass casing’ date. FYI, none of us in 1/32 Armor ever called the A2 a “starship.” The first time I saw that term linked to the A2 was on an old ESCI 1/72 scale model of it.