Back in the late 1980's, I think, I bought a couple of cappers quite similar to that one. So, I grabbed a rifle, loaded the capper with a bunch of RWS 1075 caps, and applied capper to rifle, set a cap on the nipple, pulled it away and watched with amazement as the whole capacity of the capper squirted out onto the ground. It was kind of interesting watching that happen, but not funny.
I loaded the capper again, and sure enough, it happened again. That was enough for me, back it went. I was rather disappointed. Actually pi$$ed off was more like it.
From the looks of your capper, I doubt if something like that would happen. Much finer work.
John