303 British

[Potashminer]

Actually, the "helix" is the rear face of the locking lugs and the seats within that receiver that engage those lugs - they are not vertical - they are slightly sloped, so they cam the bolt forward continually as the bolt is being lowered - most modern rifles have flat, vertical lock up lugs - some initial advance at the start of the bolt closure, but pretty much vertical for about 1/2 or more of the bolt handle closing motion. On the Lee Enfield (and P14 and M1917), the bolt face is off the cartridge case as soon as the bolt handle is lifted any amount - on a mauser or similar, have to lift bolt handle about half way before it backs off that cartridge case.
There is no "pull" to get the bolt coming backwards on opening, except at the rear end - the extraction cams. So two sets of cams - one to push the cartridge in, another to pull that bolt rearward. On a very shallow slope - you can watch the bolt advance and retreat while the bolt handle is being opened or closed - does not happen on many other designs.

 

[Potashminer]

you are absolutely right.

there are scratches on the part of the body just above where the case separation normally appears.

what does it mean

I don't consider case head separations to be "normal". Should not occur very often, if at all?? Original design was to chamber a fresh cartridge, fire and extract it and then that brass was discarded - on to another fresh cartridge. By and large, the original cartridges could withstand the multiple deformities on firing - once - without separating. Poor quality brass and grossly enlarged chambers thought necessary for wartime trench fighting conditions did result in some case head separations - was reasonably common to have a broken case extractor as part of one's field kit.

Has been posted multiple times on this site and others about using o-ring or pony tail elastic to "fire form" a new case to fit snuggly to that chamber - essentially causing the fired case to now headspace off its shoulder, instead of the rim. Lee Enfield are notorious for variability in chamber dimensions ahead of the rim - so brass fired in another chamber, can very well be "swelled" too much to fit easily into another chamber. Where the case walls have been thinned by firing and case stretch without being held tight to bolt face, would be where the most deformity would show? Those "incipient case head separations" are easily felt inside the case - straighten out a paper clip or thin mechanics wire - bend about an 1/8" or so right angle hook at the end - "scratch" along the inside of the fired brass - there will be a ring or circular groove inside the case, just in front of the solid case head - at that point the brass is pretty much done for - case head separation pretty much inevitable if it is reloaded and fired again with that groove in there. Was caused by not fire-forming that brass to that chamber, and then likely full length sizing that brass afterwards.

 

[Boltcarrier]

there are streaks both vertically and horizontally

 

[Potashminer]

My limited experience would suggest there is "stuff" in the chamber that those brass went it to or in the dies that resized that brass - both should be like a mirror inside - no marks whatsoever. Sometimes a barrel's chamber will have a sharp edge at the start, that can scratch a brass as it is being slid in there. Other than that, I have no other ideas?? Maybe re-assess how you lube your cases for resizing?? - pure WAG there, I do not know...

 

[mg34]

may be a sharp edge when you cycle the rounds into the gun, check for sharp edges. I just loaded up 100 rounds using mosin silver tip, steel plate is no match for these rounds.