How “full” was the shell? If you have too little powder, the primer can flash across the top of a half-ish-full case, causing all the powder to ignite at once-no bueno. If it was 70-80% full, it should be OK. I’m concerned that the low powder volume + mag primer may spell problems. I know W231 doesn’t take up a lot of space as it is, it’s charge volumes are kinda small normally. Proceed carefully, check each case for signs of excess pressures, and stop if anything seems odd (normal stuff, right?).
Just random thoughts from a washed-up mechanic…….
Yeah I’m gonna say it was maybe below or near half full without a bullet seated.