I had one I bought in 1981 for some reason. I'm strictly a hand gun guy as was my friend who also bought one but we got a good deal so we went with it. It was fun to shoot but expensive to reload. Couldn't use cast bullets either. We also didn't have a good place to shoot them except for the local gun shop out in the country about 30 miles away. Not only that it was the last time my friend and I would ever go out shooting together. I only took it out 3 times and put 300 rounds through it. The last time I must have not cleaned it thoroughly because twice it went fully auto on me. Just two rounds apiece but enough that it got every ones attention. I took it home, cleaned it well this time and never shot it again. I put it away in it's black "tactical" gun case in the back of the closet.
Virtually impossible for full-auto due to no cleaning, IMO. Sounds like a hammer/sear engagement issue to me. Easily fixed.