I have in the past fired low numbered '03s, and will continue to do so in the future. All of my loading for them has been with relatively low pressure cast loads, with an occasional jacketed handload of around .300 Savage ballistics. (But that is how I shoot all of my .30/06's, even "new" ones.) Nary a problem. I don't, however, blithely recommend firing them across the board. I will admit there is an element of danger, but certainly no more so than the other old guns I play with. What I choose to do shouldn't be contrived as an all-encompassing testimonial but rather that I personally don't see the bugabear lurking in the shadows. I'll not turn my back on one of the slickest most accurate milsurps out there.
(As an aside, Michael Petrov, researcher of note, ground off the lone locking lug of a Krag bolt and continued firing it remotely by utilizing just the safety lug on the bolt. He got some surprising results, reaching some astonishingly high pressures with overloads of fast burning powder before everything finally came unglued. Even then the bolt stayed in the receiver. Admittedly not germane to the discussion of the low number '03's, just an interesting anecdote concerning the safety of a sample of one Krag rifle.)