The problem lies in the fact that the flat hammer in the gun doesn't shear the plastic goop holding the strip together. This I solved by taking the whole assembly apart and putting a clean, sharp edge on the tip of the hammer along with a slight bevel downwards (to give it somewhat of a scissor edge) using a 600 grit diamond file.
My gun had been giving us trouble for months before I worked on it.
My band-aid for the problem was to grind down most of the plasic stuff before loading the points, but that just got to be too much hassle for the quantity we were using.
If this is within your capacity, do it. If not, a lot of woodworkers use these diamond files to sharpen chisels so you might ask one.
Hope this helps.
B.