I've found fireforming with full house loads in my few AI rifles results in as good accuracy and sometimes better than the subsequent reloads...
My Pre 64 300 Mag H&H of course, went out for the first time after I got it and my son was shooting it to get ready for elk season. He shot about 4 shots with my handloads and we looked at the target . You could cover all four with a dime and have change. I looked at the brass and it looked funny so we stopped shooting until I figured it out. Finally figured out that it had bee rechambered to AI and not been remarked. I went to the gunshop where my buddy got it before our trade and low and behold he had the dies setting on the shelf and he made me a good deal on them. It is still my son's favorite elk rifle and I may not get it back any time soon...
