It isn't just the magazine. You'll need a new follower, new or modified bolt stop and ejector. Might even need to have the ejection port lengthened.. All to gain .2 or so.. If it's due to the choice of a much longer bullet then maybe the expense is worth it..
BTW, that's not a full-length H&H action - what you have is a standard LA and you're trying to make it into a full-length version..
