Investigations of the output parameters of CuBr(Cu)+HBr laser systems have shown that HBr additives to the CuBr laser active medium result in an increase of the laser output power and efficiency that compares, in this case, with that of a CuBr laser with H2 additives. It has been found that the vapor of working substance are additionally produced in gas-discharge tubes (GDTs) less than 2 cm in diameter due to expulsion of copper atoms from the GDT walls by HBr. The results of simulating the kinetics of the copper vapor laser active medium with HBr additives show that the enhancement of the laser performance parameters can be explained by the processes of chemical transformation of copper from the solid phase into the gas one.