I use a medium Pachmayr Decelerator slip on on my 527M carbine to increase the length of pull. Nice, snug fit that doesn't move around. The end of the stock on my carbine measures about 1.5"x5.25", compare to your stock to see if medium will be right for you. I use a small Decelerator on my 452 Scout and Winchester 94 carbine for the same reason, again with very good results.
Also, I don't store my guns with the slip on pad in place as I have read this can affect the finish on the stock.
