Our first issue weapons were model 66's back in the early 70's. Before that we bought our own. We went to the range for familiarization training and over half of them had problems. We sent all of them (around 65) back to Smith and they came back repaired and we had no further problems with them. I didn't know much about guns or problems back then and don't remember what the problem was. Same thing happened several years later when we went to 686's but by then we had a range officer who was able to correct the problems. I've got a 686 with a "M" stamped on it but I don't remember if they did this with the repaired 66's.