Re: 300 RUM to 7MMRUM??
Other then the neck dimension they are the same. Be careful not to exceed the neck diameter of your chamber though.
If your rifle is a factory rifle this will "probably" not be an issue but it may be.
Take a measure ment of the diameter of a fired case. Then compare that to the diameter of a loaded 7mm RUM using the 300 RUM brass.
This loaded neck diameter should be at least 0.0015" less then your fired case diameter. This is minimum and I prefer a solid 0.002" smaller in diameter. This allows 0.001" neck expansion when the round is fired for the case to release the bullet.
If the loaded round does not allow this clearance, you will get into some pressure problems depending on how tight it actually is.
I suspect this will not be a problem if it is a factory pipe and generally, doing this results in a more quality cartridge to chamber fit as it tightens up the neck clearance.
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