I had a partial case head separation using a 1.8oz buffer

[muvef]

https://hodgdonreloading.com/accurate/accurate-2520r

Max charge was 29.5 / 29.6 grains

Something else happened if your case head opened up. This was an 80KPSI+ event (more like 120KPSI)! Wrong powder, wrong bullet, obstructed barrel, massive over-charge, something major happened. You don't need to simply drop your charge by a single grain.

Do you have any velocity measurements?

Re-weight your powder charges in your cases as you take them apart. Put the same powder back in your powder measure and re-weigh the charges.

Hornady says 29.1 grains is max with that combo, but both QL and GRT say that's a 64,000 plus PSI load.

Nosler says 29.5 grains with their 120 gr BT.

Weird.