The fix for .303 case stretching is to slide an O ring down the case so it rests against the rim. When the round is loaded, this ensures the case base is firmly contacting the bolt head, so any "stretch" is at the shoulders, ideal given the variability of Enfield chambers.
A much better fix is to eliminate any case stretching whatsoever before ever firing new unprimed brass. Then all that happens upon firing is that the case expands radially to contact the chamber walls, no stretching anywhere.
You do that by creating a false shoulder ahead of the factory shoulder, essentially creating the equivalent of a fire formed case without actually firing. And you now have cases for your rifle that headspace on the shoulder, not on the rim, removing any variables concerning differing rim thicknesses.
My 95L series 1950 Long Branch that still had the arsenal hang tag attached when I got it has a very short ball seat and leade (compared to most Lee Enfields) as a chamber casting shows. Look at how much further ahead on the neck the false shoulder on that modified case is when compared to an unaltered case. (best photo I could do with my phone at my bench under fluorescent lights)
The "headspace issue" for Lee Enfield rifles is with few exceptions found between the ears of unknowing American handloaders and gun writers. With SAAMI's decision that they know better than the Brits what the proper measurements are for the .303 Brit contributing as well - SAAMI dimensions for chambers, cartridges, reloading dies, headspace gauges, etc are about .005" shorter than they should be. The Go-No Go range for the .303 British is only .010" to begin with.
Everything after that first firing is neck sizing only until you get to the point where you need to bump the shoulder back a bit. I think the Lee Collet Die is best for this, but opinions may obviously differ.
This requires handloaders who have more than one rifle to segregate brass for use in each rifle.
