Reloading .303 British : Brass life expectancy ?

The condition of the case after first firing is extremely important to case life.

Before replacing bolt head and later bolt body of my No.4 annular rings caused case separation after no more than three firings despite a unusually tight chamber.

 

My chambers are fairly tight. I lucked out with the No.4, fired cases from it look almost like new unfired cases, very little slack at the shoulder. I picked my SMLE specifically because I had reloaded ammo for the previous owner and knew this rifle had a fairly tight chamber at the body, though plenty of slack at the shoulder.

Only reason I replaced bolt body and bolt head of this rifle was because a badly fitted SMLE MkI bolt head had worn out the SMLE MkIII bolt body threads.

So far I've seen no indication that a generous shoulder contributes anything to annular ringing on first firing if head gap is tight.

 

The annular rings come from the case wall grasping the chamber wall and the case head being pushed back by chamber pressure. The rim limits how far a case can move into the chamber from striker blow or primer thrust if unstaked, close headgap limits how far back the case head can move.

 

Headspace (whether a rimmed or rimless cartridge) at or under factory maximum specs of .067 will allow longer case life, all other factors being equal, so long as you don't resize the case body. Beyond .067 case life begins to suffer.

 

Grossly over sized chambers are never good for reloading, but the commonly found generous shoulder has little or nothing to do with case separations of rimmed cartridges. The rim limits forward movement of the case.

Excessive clearance at the shoulder, within sane limits at least, is only a serious factor with rimless cartridges.

 

Some like to use thin rubber O-rings around the case body above the rim to hold the case back against the bolt face on first firing. This is of value if their rifle has a very generous head gap. I have never had to use that method.