Enfield headspace issue?

[Alfred]

the HXP cases on average are 20 grains heavier than the Winchester cases and the rim of the Winchester is more rounded on the outer edge than the HXP cases.

And your cases are about thirty years apart in date of manufacture, one being from recent commercial manufacture, the other from WW2 era surplus machinery once used for military contracts.

I have an old commercial krag cartridge here whos rim is from .003 to .004 thicker than more recent production cases.

Commercial sporting rimmed ammo had thicker rims than much of the more recent production. Somewhere around here I have results of measuring the rims of a number of manufacturers, rim thickness usually at the max .064 or occasionally thicker by a few thou.

The .30-30 is a much lower pressure cartridge and rifles in that chambering aren't likely to have the generous headspace the Enfield is so well known for.
About the only things the two have in common is they are rimmed tapered cases. Might as well compare the 7.62X39 to the 7.62X25.

Winchester branded ammo can vary greatly in quality. I've had some that split lengthwise and the same type bought a year later that functioned perfectly.

I don't use Winchester cases any way I use Remington and have had no problems with those despite the thin rim, because I obtained a No.3 bolt head to get very a close head gap.

PS
Cartridge cases are not made to a single unalterable specification, Winchester Palma Match .308 cases weigh far less than other cases of the type, even other Winchester .308 cases.

There are variations over the years for one reason or another. On average a lighter case means more powder space and lower pressure for the same velocity.
External dimension must be very nearly the same, but internal dimensions are up to the load development department, to make the best use of available propellants and projectiles.


Also I just checked one of my Winchester "WW Super .303 British" cases, the rim looks nothing like the rounded rim of your cases.
Aside from the headstamp this rim is identical to that of the HXP case you've pictured.

Theres a pretty detailed breakdown of the HXP .303 on this thread.
Surplusrifleforum.com • View topic - A look inside: .303 Greek HXP-71 ammunition
With plenty of big pictures like a certain someone likes to cover threads with, but these are informative.

More info
Carteach0: .303 British, cases before and after firing, comparison
Take notice of the visible difference in the relief cut above the rim, the two cartridges bear the same headstamp and year.
This suggests worn and rebuilt WW2 surplus machinery.

Figured I might as well add this
From a site discussing the various chamberings of the strengthened "Big Bore" Winchester rifles.

Let's assume the strength of the brass is the limiting factor in max pressures. Then consider that the area of a cartridge's base increases by the square and the circumference of the case increases in a linear fashion. The circumference of the case, together with case wall thickness, determines the cross sectional area of the brass available to resist the pressure. Thus the larger diameter case has less brass per unit of base area to contain pressure and so the larger diameter case will fail at a lower pressure than the smaller case.

The smaller diameter case puts less stress on the brass.
What I'd figured but this guy explained it well.