Thank you Styrak
I dissasamblied the Hammer Trigger Set ans use a lime to remove a little bit of metal (metal Lolll should I say metal lolll ). This fixe the burst issue.
However, when I disassemblied the Sear, two little brass washer dropped on the table without seeing where they were assembled. Even in the We-tech explosion part list, they are not showed.
Do you have any idea where they are suppose to be installed?