Can't ID No4MK1 rifle ...

[Mk VII]

All Lee turnbolt actions require the spring compressing during the closing stroke of the bolt, so that is why the final inch is hard to push.
'Headspace' on Lee-Enfields, can be considered as distance between bolthead face and the recess on the rear of the barrel on which the cartridge rim sits. It is measured with proper Go/NoGo gauges, not gaffer tape, beer can shims, strips of cardboard or other expedients. Americans seem obsessed with this, perhaps because they get sold all the junk guns that are unsellable to other gun-owning countries, or maybe because it's easy to change by parts substitution (although this opens up other problems). Many of the L-Es sold in America seem to have been separated from their correct bolt over the years and this increases the likelihood of a problem.
British commercial proof marks are visible, a form of testing required by law in most nations with any sort of a gun industry, with the glaring exception of the United States.