Okay, maybe either a over-stressed rifle with a bad bolt or the loads have been excessive and the cartidge head has bulged (measure the cartridge dimensions)?

To get an idea of headspace, get a precisely made cup shaped object (pistol cartridge or Lee powder scoops work well) and put it over the neck of the case. Then measure the cartridge base to the top of the cup with a vernier. Then compare to a fired case from your rifle. The size of the cup doesn't matter as you are only after + or - relative to each other. The cup shape should be 0.4" internal diameter but it doen't have to be exact as long as you are away from the curves where the taper changes.

The difference between your rifle's fired case and the lapua brass should give you an idea of whether the shoulder on the lapua brass is forwards

If you compare a fired and sized case, this method also lets you quickly dial your sizing die in towards your chamber dimensions (so less unnecessary working of brass). Each 5 degrees of turn on a standard reloading die is almost exactly 1 thou of an inch of movement.

BB