Grimstod
Machinist, Designer, and Shooter.

I confess I have no 303 experience, need to get one, one of these days. I have 30-30 and 54r and have never seen case head separation even with FL sizing 10 times. Here is an example.

Keep in mind FL sizing with either die in these two cases results in .012 of shoulder bump and head spacing on the bolt face is less then .004, I have another gun that I just put together last winter and it has less then .002 of head spacing clearance for the bolt but I have not fired brass enough to measure a difference in the amount of stretch in the web of the cases for comparison. I will have to report back on that next year.
I did some good image searching to but every instance I found the real problem was improper head spacing.
This one for example was the first firing and he clearly has a head spacing issue.
