I got a new to me Star BM. It worked good when I got. But after shooting it a bit a problem has developed. The hammer drops to half cock when I drop the slide stop and chamber a round. The impact of the slide on the chamber causes the hammer to drop to half cock. I disassembled it and the hammer notched and sear surfaces look good, no tampering. It has always had a light trigger about 2 1/2 lbs. help