Re: .338 Lapua Mag. excessive case length ?
Good possibility that it's because you're crimping your bullets. Likely as not, you're doing this when you try to close the bolt and that long case neck is being jammed past the end of the chamber and being forced into the bullet walls, in effect, crimping them. You could be fixin' to have a truly nasty experience if this is the case. We may be older, wear glasses and out of shape, but we DO monitor our case length and make sure that this never happens. Incidentally, while I'm sure you can beat Mid Tompkins in a foot race, trust me, you'll never beat him on the firing line.
Trim your cases, and check your headspace. Bump it if you need to and consider the use of a body die from time to time, and this will all become a thing of the past.