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Having shot thousands of rounds in MIL SPEC 7.62 NATO chambers whose throat was .3100", bullets with .3082", .3084", .3086" and .3092" all shot about 1/2 MOA at 600 yards. Clearance around those bullets before they entered the barrels with .3000" bore and .3078" groove diameters didn't seem to matter. Therefore, the chamber throat diameter doesn't matter that much to me.
The harder bullets slam into the rifling, the more they'll be deformed before getting out of the barrel. Which is why folks understanding what's important for accuracy want minimum bullet jump to the rifling when it's moving the slowest on its way to the muzzle. Minimum jump to the rifling means the least amount of bullet deformation and unbalance will occur.
A friend I shot matches with years ago worked for Roy Weatherby in the 1950's and designed Weatherby's famous stocks of that era. Roy had his shop make two single-shot 9-lug actions for him and was astonished when the one used for a .300 Wby. Mag. had a standard throat/leade so standard length ammo bullets would just touch the rifling; no jump at all. While its accuracy surpassed any one of the standard Weatherby barrels, it lasted only 700 rounds before the throat/leade eroded too much. But that round receiver twisted too much from barrel torque when fired and had to be rebedded every 150 or so shots.
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