The firing is inconsistent if the plastic accessory is not firmly seated upon the nipple. And it seems this action is affected by cold temps.
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Ken, Seeing this post disturbs me greatly. I can only say with the years of experience I have had with my equipment, it seems, as it gets older it becomes even more affected by cold weather and more difficult to operate...
However it can be overcome as others have suggested, but while we are troubleshooting this, are you using the "Thang" to insert the red thingy (Pasty) on the nipple? This adds more required force to pressure the pasty on the nipple. See drawing, please note I failed to identify the nipple, but I am sure you know which one it is.. The way I used the thang was to wrap it firmly on the pasty and press against the nipple until it popped. (I know this seems cruel, but it works). I used to install the pasty on the nipple in the warm romantic heat of the wood stove prior to hitting the woods, only after I was up in the stand would I put my "load" in, remember, safety first..
I understand you are used to useing more loads than the average person, thus creating more difficulty out in the cold, well, I can't help you there as I was usually one and done... Of coarse a lot can be said of doing it right the first time!
I stand by the deal and will work with you to correct it if possible. Here are spot checks that may help.
1. Apply the pasty in the warmth of the house.
2. Have a USED pasty ready for the field, as with anything, use tends to loosen things up, the more you use it, well you get the idea.
3. Make sure no one has dry fired and damaged the nipple, if damage occurs it tends to flatten out the nipple, actually widening the point, it can make pasty application impossible.
Let me know what I can do, I'll trade you back if needed!