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

[DeNinny]

Another cause of unexpected high pressures is failure to trim the cases.

When the case mouth contacts the start of the freebore, there is no space for the neck to expand and release the bullet.

One can see much more, even double, the pressure increase we get with no jump when the mouth is pinned.

When this specific issue happens, can you see evidence of it at the mouth of the spent casing?