[Hachbak]

I do alot of Gunsmithing and I've come into a strange situation. I'm working on a winchester model 290 semi auto .22 and here's the problems:
1. Once cocked, if you pull the reciever 1/4 inch it fires
2. The safety has no effect on trigger stop, it will fire if pulled while safety is ON
3. Randomly shoots multiple times when fired. The pin has NOT been tampered with.

My first thought was wear and tear, causing slack/space between the hammer and the trigger arm. Seeing that possibility, I think if I held the trigger the seer would not catch and the gun would simply refire once the reciever cycled. Just my personal theory. Advice please?
Thanks