If you remove the foreend from the shotgun, you still have to get the action bars out of the wood. Up inside the wood, there is a castellated nut that takes a spanner wrench or the tips of a pair of needle nosed plyers if it isn't too tight. You unscrew that nut and if you're lucky, the metal tube will slide out of the forend. Then you install the new foreend and reinstall the nut.