I am suprised, but do not doubt your problem. I have hunted with en Encore ML with 150 grains of 777 in front of the 777 primers and have never had a problem at all. This has been in temps ranging from 65 to -10. You know this, but the manner in which you store and handle primers can adversely effect the reliability of them as well. I have used all of the brands of primers, 209s, 777, Kleanbore, etc, and I always get the fouling ring in my Encore. As much as I like 777 propellant, It just burns dirty, plain and simple. You might get slightly better results in some guns with sme different primers, but in the end, in my experience, you simply must take the time to clean.