I agree with Kerby, the 7 WSM would be the way to. I have done the same conversion but 300 Ultra to 300 WSM. There are a few barrels you can rethread, going from Remington Sendero to a Winchester action works by just cutting the threads down to Winchester size and making the other cuts as necessary.
IT is possible to do this but the WSM still has enough case capacity to get kind of pissy with reduced loads.
I do not think you would have a danger issue like some of the larger cases but consistancy will probably drop off some.
One thing to remember is that if youdo use reduced loads, be sure that whatever powder you use will use a charge large enough to completely cover the flash hole when the round is laying on its side.
It would take a severly reduced load not to accomplish this but some very bad thinks can happen if the powder ignited over the full length of the case and the gas is directed vertically.
Always remember that the leavier bullets are best for reduced loads, they offer more resistance to the powder for a more efficent burn and they also take up more case volume, again a plus in what your looking to do.
I would say you could get down to a 140 gr bullet at around 3000-3100 fps with good accuracy and consistancy but it may take some load development.
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