Both No.1 and No. 4 have what is called helical breeching - unlike most modern rifles - so that means the bolt face continues to advance forward as long as the bolt handle is turning down - when bolt handle is down - is the end of advance - you are at "lock up" - that was a very shallow angle of advance, so you can generate a lot of force pushing a cartridge into the chamber - cartridge was bent, oversize, dirty - will still go - what it was designed to do. So, now the extractor hook is forward of the front face of the rim of the cartridge. As you lift the bolt, the bolt face and extractor hook will start to move back, but there was space (slop) between the case rim and the extractor. That "hard stop" you are experiencing is the extractor finally hitting the front face of the cartridge rim, with something in the chamber that is tight to that cartridge - cartridge case too long and jammed in neck, cartridge too fat and jammed in chamber, cartridge bent and now jammed in chamber, and so on. For a soldier in trench or a tight spot - very important to get a shell in to fire one more time - but extraction was about "use some power" to get that cartridge out - might very well be what you are up against? Color your case and bullet entirely with jiffy marker - you will see where the colour got scraped off - will tell you where it got "tight"...