Have a look at our Reloading section, there is some information on this one.
To my knowledge, there is no preformed brass for it, and to do it yourself is a major pain in the posterior!
Also, I was not able to get the claimed velocities from it at all, despite using a very long barrel.
I think you are much better off using something like the 300 Lapua. I am not sure whether this has become a factory chambering or still a wildcat. But, even if you have to form your own brass, I would imagine the process to be much simpler than for teh 300 Phoenix.
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saeed@ emirates.net.ae
www.accuratereloading.com
I have checked the capacity of the 338 Lapua case, it is 114 grains of water.
I would pressume the 300 Lapua would be just the same case necked down to take 300 caliber bullets.
We do have a reamer for it, but we have not built any rifles for it as yet.
It will definitely have more velocity than the 300 Winchester magnum.
Our 30/404 has almost exactly the same case capacity, which I think is very close to the 300 Remington Ultra mag, so why don't you go with that one?
You can check some of our data for it on the Reloading section.
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saeed@ emirates.net.ae
www.accuratereloading.com