Thread: 223 over resized brass?

Originally Posted by Oldbloke

Another way is using your "comparator" just measure a tight or correctly sized one and the loose one.

As mentioned earlier if they are like say,, about 0.015 - .020" load up some "light" loads to fire form them.

From experience with the .308, .303 etc if the load is too light the case will not fire form and could wind up shorter than it started. The load should be no lighter than a start load. When a cartridge fires the blow from the firing pin and the primer ignition shunts the case up the front of the chamber, slightly shortening it in the process. If pressure is not high enough it just stays there. If the pressure is higher the front of the case grips the chamber and stays there and the rear of the case is forced back to the bolt face stretching it just in front of the case head. To low pressure will be easy to spot as the primer will be backed out of the case. If you want to fire form try a couple of loads to make sure you have enough pressure.
GPM.