First off, are the mag boxes you are trying Stamped E? When it comes to P14's and interchanging parts its a bit hit and miss. Winchester marked ones (W) won't work. There are two variations of the E marked ones. Some have a 2 stamped on them and they fit the receivers stamped with a 2 on the top of the receiver above the serial number. Can you post some pictures of the mag boxes you've tried?