Okay guys, here's a poser for you. I've got a Remington 700 Mountain Rifle in 280 Remington. I've started trying to work up a load for the Berger 168 gr. VLD. When I started, I found some Federal brass in my inventory. I've had this gun for a long time. It was one of the first batch of stainless Mtn. Rifles Remington made. So the brass is of unknown origin. But I full length re-sized it since that's the only die set I have for a 280, so I figured it wouldn't matter. I took 12 pieces of brass and loaded four different loads and test fired them. Before the next loading, I trimmed the cases to 2.530". I had to remove about .020"-.030". I reloaded them again with different loads and test fired them again. On the third re-sizing I noticed one case had a partial case head separation. I checked the remaining 11 cases and found that they were getting ready to separate also. I felt the thin area with a hooked wire and could see it with a flashlight. I trashed the cases. There were about 30 more pieces of brass in the MTM box so as a precaution, I checked them too. They also had thin spots so I threw them away too. Okay, so now I'm wondering if the brass was fired in my rifle originally and if so, did my rifle have a problem. I checked 10 Remington brass on hand and it was okay. The only other brass I have is Nickle in both Federal and Winchester. This brass checked okay also. I think it was fired in my rifle but not positive. I have 4 empty nickle cases from factory Winchester loads that I fired last weekend to sight the rifle in that I know are once-fired in my gun. I started taking measurements to see if I can find the problem, if there is one. The new un-fired Winchester brass measures 2.531" base-to-mouth and 2.163" base-to-shoulder. A fired case measures 2.534" base-to-mouth" and 2.169" base-to-shoulder. Nothing too bad. The case length grew .003" and the shoulder moved forward .006". Okay, now is where my questions come in. I re-sized one of the fired cases in a Lyman full length sizing die with a carbide expander button, lubricated with Imperial sizing die wax. I measure the sized case. The base-to-shoulder length is now 2.159", .004" shorter than factory. Maybe a problem since the next firing will be .010" growth at the shoulder. Next I measure the re-sized case length and its now 3.554". The case has grown .020" in length from being sized one time. Here's my questions: Are any of those measurements out of line and could they be the reason the cases separated? Let me add that the brass just below the shoulder expanded .008" and the brass seemed hard to re-size on my Rock Chucker IV press. Any thoughts or suggestions?