O.K.--I guess I'll embarrass myself and also help someone else to avoid the situation. About 1984 I attended a match at the Saugus, CA, range to qualify to buy an M1 from DCM. There was virtually no restrictions on rifle or caliber, except that it had to be something larger than .22 LR. I took a 180-series Mini-14. I got slinged up and eased myself down into the prone position. Everyone could tell that I'd shot before, and the Range Master and a club official came over and stood right behind me to watch me clean the target. I started firing, heard comments of approval, but after about the 10th shot everyone left and were watching someone else. I qualified, but it was a close thing, and later my buddy said, "I don't know what happened. You were doing so good, and then you just walked off the target." Much later, at home cleaning the rifle, I discovered that the spring loaded pin that holds the elevation wheel in place was missing. Reading up on it I learned that it was a common bug of the 180-series, that the pin was too small in diameter to withstand too much recoil, and the bug had been worked out by substituting a pin out of one of the later series that was larger. Once the pin went bye-bye each subsequent shot caused the elevation wheel to advance one notch.
The fellow that won the match was using a Win. Mod. 94!