No.4 Mk1 chamber flaw...

[badge176]

A shooting buddy got himself a sporterized No.4 Mk1 in .303Br and we finally got to the range yesterday. Unfortunately upon each firing, the bolt would rotate but resist traveling back. We did get three fired and out and I quickly found the raised rib that had extruded part of the circumference of the neck (almost to the case mouth) where there's obviously a gouge in the chamber. So what to do?

trim cases back so they don't extrude into the grove, that'll leave less neck to hold the boolit...
get it re bored to .35-03?
rebarrel it?

opinions, ideas...

[Outpost75]

The Brits condemned a large number of No.4 rifles which developed cracks in the chamber area, due to a metalurgical flaw. I would find a gunsmith who can carefully inspect the chamber with an optical borescope to assess the damage. The safest path is to rebarrel unless you can get the barrel magnetic particle inspected using the wet method with continuous circular magnetization. Unless you have a way to have this done on the cheap, it would be safer and less expensive to replace the barrel.

[Green Lizzard]

set it back 1 turn and rechamber

[Multigunner]

Over torqueing of barrels that had not been properly fitted at the shoulder caused stress lines that resulted in deformation of the front of the chamber on proof test firings. So long as the rifle still operated safely they let them pass, since head spacing on the rim made the fit at shoulder less important.
This may be why this deformation occurred. Later on they developed a breeching washer system to make fitting barrels faster and avoid over torqueing.

I would look for a replacement barrel and have it properly fitted. Cracks can only get worse.