Thread: Is this normal for my brass

Originally Posted by veitnamcam

Almost correct, what causes case head separation in that area is not actually anything to do with the die working the brass in that area....the die actually sizes very little near the case head.
What actually causes case head separation in 90% of cases is excessive head space, that doesn't mean the rifle is large chambered or has excessive head space (tho the latter could contribute if the re loader is unaware of "headspace" )

When a cartridge is fired it is driven forward by the firing pin hitting the primer thus taking up any "slack" in the chamber/headspace.

Primer and powder ignite and pressure rises in the case, the thinnest "brass" of the case generally the neck expands and seals against the chamber first and grips the chamber.
As the pressure builds the case stretches out to the chamber walls and grips them untill the much thicker case web and base can no longer expand and are driven rearward until held in place by the bolt face....the gap from bolt face to brass is effective headspace and the brass will stretch that amount (generally with a few caveats) every firing and 99 percent of it in that case head/web junction.

So that is where all the stretch happens hence the separation, nothing to do with (correctly set) dies

Yes This Above.
So to summarise, if the case has been sized so that it is too short for the particular chamber when it stretches at firing there can be separation. Which means that the 'ideal' case length and sizing for a bolt action is when the case 'just' chambers with no excess play. So neck sizing and bumping the shoulder back just a little if you have to. Lever Actions more tricky to get right which is why lever hunters should only use Savage 99's