Weatherby Freebore

do you mean measure your chamber?

You can't free bore it, a gunsmith has to, a gunsmith could also easily measure for it.  It might be free-bored already, you'd need a Stoney Point/Hornady OAL case guage and the modified 30-378 case for same.  A call or E-mail to Sako's US office might also tell you what you need to know.  If your chamber's been cut with no free-bore you'll have to back way off of max charges as the data in loading books will assume the free bore is present.

freebore-sometimes called throating.the removal of the riflings at the chamber you have to measure it first as Clay said. It is best to load a dummy cartridge to fit the magazine and then chamber it and if the bolt closes without pressure load it up. If not then have a good gunsmith remove some riflings to match the dummy cartridge If you do not then it is hello high pressure. .010 difference in gun freebore can increase  to10,000psi real quick.. Or fit the bullet in the case and use either a candle or a sharpie then close the bolt once the bolt is opened the bullet will show rifle contact on the bullet. Measure it and compare to factory max length if it is shorter than manuf. spects then chenck if it goes in the magazine if it fits both places it is ok for than bullet but not all bullets have the same ogive which will increase pressure. You can cast the chamber and then you will know exactally what the measurements are,then you can have a reamer ground for the measurements and ream your own die to match the chamber.