Notwithstanding that some lighter bullets don't feed so well in some Model 1903 Mannlicher's, mine loads and shoots 140 grain Nosler partitions just fine. Also 129 grain Hornady spire points. The best bullets have been 159-grain Hornady round nose however. Lately I've been using 159 grain Cacarno bullets. I don't suggest you do this yourself unless you, (1) get a gunsmith to slug the bore and prove it is oversize and (2) get a Stoney-Point, (now Hornady) Overall Length Gauge and work out the right seating depth. It's nothing like the SAAMI overall length but much shorter. If you don't want to be bothered with this, just use regular .264 (6.5mm)bullets and accept a slight velocity decrease due to gas blow-by.
Post 1945 M.1903'a are probably .264" and pre-war would probably be oversize, but assume nothing until you've proven it with Cerrosafe.
My full-stocked carbine, BTW, shoots a tight group in 5-shot rapid fire just as well as 1-min spaced shots. No suggestion of walking the impact. Also, you may find some European 6.5mm bullets are undersize, not even .264". You can imagine what that does for velocity and accuracy. So break out the vernier and start measuring. If you want to use them anyway, you may need to turn down a spare expander button a thou or two, so the neck grips the smaller bullet. Don't mix up the 2 expanders, use a dab of paint on the stem to identify the smaller button.
Good luck.
