I am no reloading expert but have been reloading all my ammo for .22-250 and .243 for years. Initially I worked out a load for both rifles and have stuck with that both rifles being as accurate as suits my wants. (within 1/2" at 100yds)
My regime is to use the same cases about 5 times, neck size the cases, clean using ultrasound cleaner and case tumbler, resize the case length (where necessary) and chamfer. Through this I have never had a single problem.
My mate has recently started to reload for his .243. He obtains once fired Norma cases from a relative. These cases fit his rifle without full length resizing. He loads the cases using almost the same load as I use and they are accurate. The bolt cloases over no problem and after firing the case ejects no problem. But, after being neck sized, cleaned and the case length checked they will not go back into the rifle. My simplistic view is that they came out of there they should be able to go back in.
Any suggestions as to the cause?