There is a whole bunch of threads over on Gunboards regarding brass segregation and neck resizing relating to the .303 British cartridge. Some even go so far as to use O-rings with the first firing of new brass to ensure that the case head is firmly seated against the bolt head. That blows out the shoulder to match that of the gun. Shoulder length and taper can be inconsistent on SMLEs, No4s and maybe even Pattern 14s. For sure, I wouldn't rely on them being all the same.

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