I changed again the Barrel Seal for a new one and put a new Brass shim and a new S610H Seal. The problem still remains. Lots of air coming out off the breach hitting me in the face

Hi Guys. I have an AA S500 FAC 4.5mm 30 Joules. I have a problem with air rushing from the breech back to my face after each Shot. I thought it was the barrel Seal so i changed it with a new one. Part Number FP121. But the problem still continues and im thinking the loading bolt could be thinner and...