Considering getting into reloading (303, 6.5x55, 30-06)

[Archer1971]

I've been tempted by reloading for my milsurps for a while now (I have three 303s - soon to be four - a Swedish Mauser, and about to get a 1903A3, fingers crossed).

I've been keeping my brass for the last few years in case I do so have a fair box of .303, mainly PPU once fired. My question is that I expected each chamber to be slightly different, so that once I start reloading I'd want to keep brass from each rifle seperate (which I've not done so far). Testing shows, though, that some of the brass now won't chamber in any of the .303s - but it must have been fired from one of them! (My range is closed lanes, so I will only have picked up my own fired cases).

How can that be? For the ones that won't, fit the bolt won't go all the way forward, so I'm assuming the shoulder has moved forward.

I'm a complete novice (in fact not even started) in reloading so I may be missing something entirely obvious!