Greetings again,
I have done a fair bit of weighing .308 W cases over the years and together with data mostly from Handloader mag have found the following. Kiwijames my weighing of Lapua brass marked 7.62 x 51 and 308 Win is much the same as your results of around 173 grains. This is a little heavier than Remington and Winchester recent production but lighter than Federal which is about the same as LC 81. The Lapua brass also has a slightly larger head diameter so some of that extra weight is here. There is a strong correlation between weight and case capacity. Other than a larger diameter head or differences in the rim recess size can have an effect on these in new unfired brass. In fired brass all bets are of because the size of the chamber has an effect. Handloader data showed capacity of between 53.4 and 54 grains of water for Remington and Federal cases. Winchester cases held more but more recent production is heavier, close to Remington. Measuring case capacity with water is a little hit and miss as any air bubbles will give a false (low) reading. All in all I don't believe your bolt problems are due to case volume. Also I would be very surprised if any Lapua military cases are head stamped 308 Win. The presence of the stab crimps may be needed due to non toxic primers. It would be interesting to know what the original rounds were.
One thing that you may wish to check is if the projectiles are close to or touching the rifling. For hunting ammunition there should be at least .05 mm (.020 inches) of jump. Hunting projectiles vary slightly. If they are too close the odd one may touch giving a pressure spike.
Regards Grandpamac.