I couldn’t find 6GT brass when I needed it so I picked up 100 rounds of factory Hornady 109s. Shooting them in a Seekins Havak Hit.
They are shooting sub half MOA. ES numbers are crazy high and almost half are nearly piercing the primers. The other rounds don’t seem to have any pressure signs.
I’m going to load my own later this week and see what happens but I have four more boxes to shoot.

Ammo or rifle the culprit?

Maybe an overenthusiastic firing pin strike or excessive firing pin protrusion? It doesn't look like a pressure issue. Maybe even thin primer cups?

I've got a single shot rifle in 9mm Para that will do that with some factory rounds (S&B I think) but is otherwise normal in my pistol. Mine leaves dirty firing pin marks but I think it's only a split and not a complete disc punch like yours seems to be.

So the answer to your question may be - a bit of both. See what reloads do.

Firing pin hole is probably oversized