# 300 win mag to 300 RUM



## meleagris (Dec 13, 2009)

I was interested in converting a 300 win mag to 300 RUM.  Can this be done by reaming the 300 win mag barrel with a 300 RUM reamer and no other modifications assuming that the magazine is long enough to handle the RUM?  If so, does anyone know of a reliable gunsmith that can do this?


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## Hammack (Dec 13, 2009)

Well it may or may not be possible.  What type action is it?  IF the original chamber is cut fairly concentric then the 300 RUM reamer will cut out all of the original chamber.  However there are a few things to consider.  The cost of removing a barrel setting it up and the rechambering and headspaceing is gonna be substantial.  Unless I was doing the work myself, as I do, I would recommend buying an aftermarket barrel and having it chambered for the RUM.  I will also add that in my experience I have found that factory chambers are often not concentric.  I have bought several take off barrels over the years with intentions of rechambering them to another cartridge to only discover once I got some of them in the lathe that the chamber had so much runout that I could not rechamber.  If I dialed in on the threads and shoulder the chamber was off.  If I set up on the chamber then everything else was off.  I have been told that a floating reamer holder will work in that situation, but then you end right back up with a chamber that isn't concentric.  Which is gonna result in poor accuracy.  Also, keep in mind that you may have to file the feed rails to make the cartridge feed reliably thru the action.  Just some things to keep in mind.


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## germag (Dec 13, 2009)

Is the bolt face the same? The .300 RUM is based on a .404 Jeffrey case and the .300 Win Mag is based on a .300 H&H Mag.


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## Hammack (Dec 14, 2009)

germag said:


> Is the bolt face the same? The .300 RUM is based on a .404 Jeffrey case and the .300 Win Mag is based on a .300 H&H Mag.



Germag, the Jeffrey case does have a slightly larger case head diameter.  If I remember correctly it was about .005", but it should work in the standard magnum bolts.  I have done two 7mm ultra mags using standard 700 magnum actions, and it wasn't a problem.  I personally just don't think i would pay to have a factory barrel rechambered considering the cost.  I use alot of factory 700 barrels to rechamber, but I do all my own work, and can get them cheaply to experiment with.


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## germag (Dec 14, 2009)

Hammack said:


> Germag, the Jeffrey case does have a slightly larger case head diameter.  If I remember correctly it was about .005", but it should work in the standard magnum bolts.  I have done two 7mm ultra mags using standard 700 magnum actions, and it wasn't a problem.  I personally just don't think i would pay to have a factory barrel rechambered considering the cost.  I use alot of factory 700 barrels to rechamber, but I do all my own work, and can get them cheaply to experiment with.



Yeah, I agree with that. It might be worth it if you are just going to have a barrel re-reamed and set back to take up throat erosion or something as long as the bore isn't shot out....I'm not sure I'd go to the expense of paying someone else to re-ream from one cartridge to another.


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## meleagris (Dec 14, 2009)

Thanks for the info guys.


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