I've had a total of 4 diffrent Weatherby rifles and each of them, no matter the caliber had long throats. This was originally used on their line of Magnum cartridges but it appears that they do it to all chambers. To check this out you may need to get a longer bullet to check out the legnth of the throat or get a device to measure it.
I like the Stony Point OAL Gauge, they have modified cases for most all standard factory loaded cartridges and will modify any wildcat case that you send them.
Another way that I have used in the past is to load a flatbase bullet backwards and slowly increase the seating depth until the bolt closes. This will get you in the ballpark if used in conjunction with a Sinclair comparitator.
You will probably need to go to a bit heavier/longer bullet to achieve your goal, but then again a consistant .69" is less than 3/4 MOA and should put most critters in a wee bit of danger!!