Ok, so there are the popular .22 conversion kits for AR’s, 1911’s, and other handguns.  Out side of those I have read about other sub-cal devices such as a barrel insert for a 12ga. to shoot 9mm, or a smaller device that allows a .32 to be fired from a .308 rifle.  Does any one know if they exist, who makes them, how to get them?  Has anyone used any devices like this?  If so what was you experience?  Thanks in advance for you posts.