Gap between barrel and receiver

[Bruce_in_Oz]

Just for the record:

SMLEs breech up on the INNER breech ring; that is, the inner ring where the bolt head seats.

No.4s, however, breech on the front face of the receiver. Then there are the 7.62 NATO converted No4s that use breeching washers between the receiver and Knox form.

NOTE ALSO that Mauser 98s are also SUPPOSED to breech on their internal ring AND have 55deg Whitworth- form threads. Few, if any, commercial barrel-makers around the place seem to follow either of these practices.

A SMALL gap between the receiver and Knox form on a SMLE should be OK; on a No4, probably not. I understand that it has something to do with both the theories/observations of thread-crush and the manner of gauging used to select components.