rs I am assuming you mean primarily in America and when I hear a term like "in" I think or equate it with "what's in style TODAY or of late". IMHO the old veterans like 30/06, 270, 308, 243, 7mag I wouldn't call them "in" so much as I would call them "old standards". They've been around long enough and have a long enough following to surpass a fad or be "in style".
IMHO the more "in" cartridge right now would be the 300WSM. I personally think it will be around with us for awhile and just might become part of that "old standard" list, but only time will tell. I suppose another arguement for cartridges that are "in" right now are the various super-mags like the RUMs, 30-378 and a few 308 Warbirds (hmmm I'm kinda partial too that last one myself!
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Time DO tell,
RA