Currently I have the box with duct seal putty - it works perfectly for the individual shots, but once hits start to accumulate around 10-ring - pellets start hitting each other, pieces of lead flying around, etc. etc..
Anyone can suggest a better setup?
(I am thinking about piece of thick heavy rubber (e.g. tire), free-hanging by the top. So when pellet hits the bottom part - it will not penetrate it, but lose energy to swing the rubber, and then just drop down)
This is what I have in the beginning:

And this is in the end:
