I was searching my latest Brownells catalog looking for a looking for an inexpensive AR mag to use to fill the AR magwell, and I came across a product that I haven't seen mentioned here before. It is called the "Jimmy Plug" made by Blindhogg Products, it is a plastic plug with a neoprene seal so that debris doesn't enter your lower through the magwell. I am not associated with the company, Just thought some of you Guys would be interested. Shoot Straight Moondo
Here is their site.
Jimmy Plug - Magwell Filler