PUMA and other variants have problems after ammuniton rack gets it and burns. Even after repairing at the last mag it fires from client but does no damage nor hit mark.
You can bug report it here: Gaijin.net // Issues (just search a bit first so that you don’t report something that is already reported and known about)
A guide on how to report bugs can be found here: ([Navigation] Technical Knowledge Base | War Thunder Wiki)