class CfgWeapons
{
class Default {};
class Shell105 : Default {};
class Shell_LT : Shell105
....
class Gun105 : Default {};
class Gun_LT : Gun105
is wrong, use
class CfgWeapons
{
class Default {};
class Shell73 : Default {};
class Shell105 : Shell73 {};
class Shell_LT : Shell105
.....
class Gun73 : Default {};
class Gun105 : Gun73 {};
class Gun_LT : Gun105
instead