The Speer #14 Reloading Manual includes cartridge drawings with referenced dimensions used by the U.S. firearms industry. Check your cases against these numbers:
Case diameter 0.200" from the base- 0.4698"
Case diameter 1.850" from the base- 0.4426"
If your sizing die is not accomplishing this with the Lapua cases, what about sizing them with an RCBS Small Base sizing die?
ETA- I type too slow, just check them against the drawing that Dean2 posted.