I had to resurrect this old thread. I tried the duct tape method, but had problems with stock adjustment and decided to look for a better alternative.
The solution I came up with was to cut a 1 1/2 - 2" section of rubber bicycle inner tube to cover the gap between the stock and the buffer tube. Remove the stock, slide the piece of inner tube over the leading edge of the stock and reattach the stock. Pull the inner tube forward until it covers a portion of the buffer tube.
Now your stock is still adjustable and the solution highly satisfactory without that painful "pull"!
It's called the "Tactical Beard Guard." I suppose if some company was marketing this, it would cost $9.95.
My gift to all the beard wearing patrons of CGN and it's FREE! Let me know how it works for you.....