Today at the range my wife, son and I were shooting a variety of different loads in different rifles to prepare for Prarie Dog season. I was trying to fire-form brass for my new 6-5 284 and we were doing load development in a 204, 17 Fireball, and my sons 260AI. My son had just picked up his rifle to clean it and allow it to cool and I took the opportunity to fireform a few rounds in my rifle. I asked my wife if she wanted to shoot it and she said she did so she sat down chambered one of my sons 260AI rounds in my 284 and fired it. After the she cleared the empty she said "my this case looks funny". I looked at the round and at first didn't understand what had happened. The case looked like a 284 case with a short neck then I looked at the rim and realized what had happened. Can you believe it didn't seperate. Lapua makes great brass. If I can ever figure out how to post pics. I'll post a pic and you guys can see what stupid looks like. I never thought that this could happen. If you hold up the two rounds the 260AI is shorter than a 6.5-284 but apparantly Murphy is alive and well in Colorado. And to add to the odd part the bullet impacted right with the other fireforming rounds. Go figure. In the future when we take a rifle off the bench we will also take the loaded rounds off of the bench.