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We’re occasionally asked to supply headspace gauges for checking 7.65×53 (Argentine) rifles. In these instances, we decline the request to make the gauges and this leaves our customers wondering why—this is written to explain our rationale for doing so.
There is a significant difference between the modern (CIP) headspace dimension for 7.65×53 and the headspace dimension of military rifles manufactured early in the last century.
If you use a minimum headspace gauge made to current CIP specs to check an all-original rifle in good shape, you’ll find the gauge indicates the chamber is short by approximately .020”. We’ve checked many all-original rifles, from different production years and have found a similar headspace difference in all of them. Obviously, something has changed.
If we had access to original, factory specifications for the dimensions to which these rifles were made, we’d be able to make gauges with confidence they were correct. Absent this information, we choose not to make them, because their use could cause original rifles to be altered, unnecessarily, to the new, longer spec.
How does Norma—who makes ammunition for the 7.65×53—cope with the headspace difference between old and new chambers? They form a large radius at the neck/shoulder junction of the cartridge.
In the old, shorter military rifles, this radius will crush sufficiently to allow the bolt to close and will hold the round securely when in battery. In rifles headspaced to the new, longer spec, the neck/ shoulder junction of the chamber contacts the cartridge a little further forward, but will hold the round securely enough for it to fire safely—essentially fireforming to the longer chamber.
We regret this doesn’t answer the question of how to check headspace in older rifles. Fortunately, 7.65×53 is the only fairly common caliber we know of which has this problem. If you have any information, or original dimensions, that could help resolve this issue, we’d be very grateful if you’d share it with us.