Belts are a pain in the posterier, unless needed, as in the .458 and .450 Marlin. Even in the H&H ctgs., there is sufficient shoulder for headspacing, but not for hamfisted handloaders, or sloppy factory ammo.
; The problem with belts, Malin's new ctg. aside(haven't measured any of those), is that headspace containment with them is lousey to say the least. For expample, most rimless cases have a SAAMI standard of +.006" maximum headspace for factory rifles and ammo. The belts on today's magnum ctgs. varies from .012" to .024" difference, a full .012" slop being allowed, double alowable headspace for rimless rounds. When one fires a round with excessive headspace, the cast stretches from just above the case web, to shove the shoulder against the chamber's shoulder, located up to .012" ahead of the case's. If one relies on the belt for headspacing and subsequently shoves that new shoudler back when reloading it, it against stretches forward upon firing and one suffers short life from the cases as they split above the case web. This is why some people only get 2 or 3 firings form their belted wonders. It is excessive headspace that causes case head separations, not high pressure. We hates belted cases. All bottle/necked rounds should be rimless.
; Aussie Mike knows.
; The rim of a belted case has a nominal measurement of .532" standard. That can and does vary slighlty, as to case manufacture. As the head diameter of a case with the belt turned off being .513" or less, even down to .505" (depending on mfg'r's own standards - some are as loose as Loosee), the larger rim is captured by a close fitting extractor of the Flanged-ctg. chambered rifle.
: I would NOT shoot a non-belted case in a belted chamber with anything but a squib load, probably only with "Light" cast bullet loads.
: If .375H&H brass with belts turned off, properly fit the .375 Flanged chamber, I see no problems with using that brass for practise. I would, however use only flanged brass for 'serious' work, as the remaining rim of a previously belted case is not very large and if one was a bit sticky, or the extractor a bit wobbly, it might slip due to only .010" to .015" purchase per side.