I have recently come across a Webley Mark II Service rifle with a few anomalies at the breech portion of the barrel that I have not seen previously on any other Mark II rifles. The barrel is original to the gun, based on the matching serial numbers, and the gun is in fairly nice overall condition.

The most obvious oddity is a small step in the barrel diameter, about 3/32” long, just ahead of the undercut for the breech nut. This is the first time I have seen this small step on a Mark II rifle barrel. How common (or uncommon) is this?
Note as well that the intercepting sear has a radius at the rear. I know of only one other Mark II Service that has a similar intercepting sear. User modification, or aftermarket item with the maker's personal touch?



The next anomaly is the treatment of the breech face on this gun.
Picture “A” shows the usual treatment of the breech face, or at least the one that I am most accustomed to seeing. The breech face is undercut from the OD, and the ID, with a narrow ridge remaining to engage the sealing washer.



Picture “B” shows what appears to be an anomaly, in that there is no undercut from the ID, but rather, a largish chamfer into the bore, with a fairly broad ridge to engage the sealing washer.
Is it possible that this barrel missed a step in the machining process, and was overlooked by quality control inspection before being dispatched?