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tobpnr, the barrel's gonna whip and vibrate the same for every shot; it's got the same "harmonics" which are multiples of its resonant frequency for every shot. It's metalurgy doesn't change 'cause it's shape is the same for every shot. But the amplitude the muzzle axis swings through will vary with the amount of powder used.
But the pressure curve for best accuracy has to be the same (within reasonably tolerances) for each shot. It doesn't have to produce the same muzzle velocity of a given lot of other ammo that shoots great. As long as that pressure curve's the same size and shape for every round, the bullet's going to leave at the same place in the barrel's vertical whip and vibration cycle. That pressure curve may well be a slightly different shape and size than the reference ammo' bullet produces, but as long as its repeatable for that same bullet, good accuracy will happen.
There's probably 2 or 3 different powders that could produce the same accuracy as Federal's .308 match ammo. The charge weigh won't be the same and neither will the pressure curves or muzzle velocity be. But as long as everything's repeatable and the bullet leaves the barrel at the right time, excellent accuracy will happen.
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