According to the CIP standards, all the 308 family are the same measurement to the base of the shoulder (1.5598 inches), but the measurement to the top of the shoulder/base of neck varies (which makes sense as all have the same shoulder angle, so shoulder continues further to narrow down to a smaller diameter):
243 1.8043
260 1.7756
7mm08 1.7508
308 1.7118
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