The reduced load is only to check for case seperation after 3 or so reloadings. No need to even check accuracy. The fact the cases drop out and go back in easily is a good thing, although it could also mean a max sized chamber (most lever action rifles have somewhat over sized chambers due to the low leverage for case extraction... I've no idea if that's a possibility with your action). I would try (after the low pressure rounds, if it works out ok) not bumping the shoulder at all and just neck sizing the brass just enough to hold the bullet (don't load up 50 of them without checking to see if they chamber first! Don't ask me how I know this!). I do that on a buddies 8mm and while they look awfully funny, with a decent and obvious bulge near the base of the neck, they chamber and shoot just fine and I get a lot of loads out of each case. This rifle, by the way, shouldn't shoot anything better than minute of earth! The first time he had it at my house I ran a cloth patch down the barrel to see how dirty it was. It felt funny and by the time it came out the muzzle the patch was torn to shreds! It's a stock K98 (I think; it's a German WWII bolt rifle) but when I put my scope in the barrel it looked worse than my gravel driveway... much worse! But he has no trouble killing deer with it, which is all he's interested in, so I'm certainly not going to tell him it can't shoot!
Anyway, if your rounds will chamber without needing a shoulder bump, that might help with the seperations. My custom .308 is like that, I can usually get 4 or 5 loadings, depending on how crazy I get with the loads, before I need to bump the shoulder, and it has a tight chamber. While I've measured it, like a lot of things, I really don't much care how much I have to bump the shoulder, it just has to chamber easily. That's the only explanation I have for my friends 22-250 case life. While I have to FL resize and go hard over center to get them to chamber after firing, it must not be bumping the shoulder back very much or the case life would be 2 or 3 loadings then they'd be scrape, like with my .243. Both of my .243's have been factory chambers and both gave me fits! My 1st .243 was a Ruger 77V heavy barrel and while case life was terrible, it was my first sub .5" rifle, too. It's now a .22 CHeetah, which I dearly love but it needs a new barrel as the throat is gone. Neck sizing for that one is another case saver!
Give the low pressure loads a try and see what happens. If they still seperate at the head, it's an oversize chamber or loose tolerance head space thing. At least you'll know if you have to buy lots and lots of brass or not!
Good luck!
Cheers,
crkckr