It would pay you to start with a custom action,stiller,lawton,bat etc all of these brands have an action designed to suit the 338 lap, it's not worth stuffing around with a factory action there are a few mods involved you will have to open up the bolt face have a new extractor put in, open the feed rails on the action and thats before having it trued so it isn't much cheaper than a custom action which is beefed up to handle the 338 lap power.just my 2 cents i have been there and done it though!