Do not sand the side of the action. That isn't what causes it to be tight. The lug under the forearm is too tight. It can be filed very small amounts at a time to get the feel you want. Just get a fine file and work the back flat side of the barrel lug and replace the forearm until you get it how you want it. It doesn't take much so do little bits at a time. After you get it where you like it, get a bottle of birchwood casey cold blue and reblue the lug where you filed it.