Tar 21 a few issues

[Gunzerker2120]

hey guys i have recently aquired a Tar 21 i have skirmished it twice it runs really well but its been having a few issues

1. Semi auto is very sometimes it fires perfectly sometimes it fires in full auto and sometimes it doesn't fire at all

2. sometimes i fire 2 shots at once or the BB's fire but they fall really short

has anyone else had these problems ? how did you fix them ?

Cheers all
Mal