Looking for a non-permanent auxiliary shell holder that could be used on the stock of my 12ga 11-87. It won't live on the gun, but will sit in a BOB-type kit "just in case." I have tried the regular slip-on units like the Uncle Mikes but they are very unstable, so I'm thinking something more along the lines of the Specter brand unit ( LINK ). Any other suggestions? Obvious I hope this will never be needed but if it is, it MUST function; therefore a balance of quality/cost and economics is necessary...