Consider the US Kragicon:

ONE, (count 'em) actual locking lug.

A seriously cut-away action body.

A cartridge of similar construction and performance to the .303.

Were they prone to rupture, distortion or detonation in their service life?

So, extending the agony of the "Lee Enfield stretch" caper, I offer the following.

The body of your basic L E is seriously solid on the left side and somewhat more skimpy on the right.

The bolt, on the other hand has a massive "reinforcing' lug on the right side and a tiny one on the left.

The right side bearing shoulder on the right is a substantial lump of metal; on the left it is a tiny nub of steel in a milled-out pocket that can, at MAX offer about 2mm square of contact surface, on a good day.

The bolt body is essentially a thin-walled tube with that long lug integrally formed on the RHS. In "compression" as experienced in firing, the side with the big reinforcing lug will display less elastic deformation than the "plain" side.

This brings us to the No4 and the "lightening slot" in the long RHS bolt lug. Getting into voodoo hypotheses here, but could it be that the "lightening" cut was not just to save a few grammes of steel, but to partially "equalize" the elastic deformation in compression of the bolt body, thus reducing the lateral flex?

The "long" lug is long, not for a massive added margin in resisting recoil, but because all that forward length is there to stabilize the bolt (preventing rotation) as it is fully retracted during cycling. This is somewhat simpler than the lug guides in a Mauser body and more robust than a simple stud 'n' bolt-groove system as seen in several designs like the Remington 788.
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