Hornady makes a .321" 170gr. with small FN for the .32 Special.

There are a number of possibilities.

Might be flow at the bolt face. Not a pressure item, but a rough bold face shearing off or re-seating primer material can cause this?

Too - rough or annealed bolt rear angle slide(cokcing portion) of the bolt will gall and cause lifting problems. This happens when improperly shielded bolts have the bolt handle changed to clear a scope.

Too-high pressure is probably not one of the problems, especially with factory ammo, even though pressure appears to be the problem. If .323" bullets easily slide into fired brass, NP, even in the .32145" groove diameter.

What do the fired cases measure for length compared to what they measure prior to firing?

Has the headspace been checked?

This forming ridge upon firing intrigues me.

A chamber case should have shown the cause.

It is not normal for brass to flow forward into the leade/freebore or as has been called above, the barrel. Not even grossly excessive pressure causes this in any gun I've seen.

Excessive bolt thrust can cause bolt binding due to an excessive headspace situation.

Rough chamber also causes hard extraction to 'break' the case free into rear-ward movement.