The 7mmRUM is an over bore round as is the 300RUM , the 7 will wear out the barrel faster and will be more finikey than the 300 simply do to being more over bore , a 257RUM would be even worse!!
If you plan to shoot the highest BC bullets out their the 7 will probably will but if you could get the 240gr Sierra Match King to shoot to 2900fps from a Sendero that would make a VERY hard hitting long range round but the 180 Berger has a very high BC for its weight and will shoot very flat. But like it was said before the 300RUM will have longer barrel life and will be less pickey about what it eats.
Now if you can find a 338 RUM in the Sendero rifle its a pretty simple job to rechamber to 338 Edge , then you woul have higher BC bullets longer barrel life and more energy on target down range.
If the two gus you have to choose from are the 7RUM and the 300RUM , my vote goes to the 300RUM , try the 240gr SMK's and if they shoot work with those if not work with the 229SMK's or 210 Bergers. Not saying that the 7mmRUM is finiky I'm just saying that the chances of it be more finikey than the 300RUM are good simply due to bore to powder ratio.
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