Since there is such a wide variation in chamber sizes in the milsurps chambered for the .303B, I think the best way to approach loading for them is the same way you would for any wildcat. FL sizing kills the brass, and unless you wanted to go to the expense of having a custom FL die made to the specs of the chamber, use of them is best avoided and one must keep the brass for each rifle separateand rely on neck sizing, however you can accomplish it.
One of the reasons why the .303 bolt rifles have such a good reputation for battlefield reliability is their overly generous chambers will feed just about anything put through them. I like the "bolt action Glock", Al! But, like the Glock, the ammunition was never meant to be reused, the rifles never meant to be fired with reloads, and so were not designed to be reload friendly - they just had to work - and work every time - with issued ammo. And on top of everything else, the case is rimmed. That the rifles feed anything at all I consider a minor miracle and certainly a triumph of engineering.
WWI accounts of Springfields with their better accuracy and tighter chambers in the mud of the trenches were sobering. Much, much worse for jamming up than the early M16's in Viet Nam. But the old .303's were, in comparison, relatively trouble free. The Brittish and Germans (who had the time to think and prepare) both used basically the same rifles in WWII, but we had to upgrade to something that would be more reliable in nasty conditions. I'm not dissing Springfields, just trying to illustrate that what makes the old .303's such a PITA now for handloaders are arguably one of the reasons why you aren't reading this in German.