msalm; I would go with the .338 RUM chamber also. It's got plenty of power for what you want to do and factory brass, ammo, reamer, and headspace gauges are available. I'm partial to the .338 X .378 Wby factory chamber, but you would have to open up the bolt face on your Nesika. I've never seen one, so I don't know what you would have to do to the extractor.
Is the Rock barrel a 28" blank? If it is, you can still finish at around 27 1/4". With that barrel length, 2750 fps should be reasonable with the 300gr SMKHP. I chronographed my .338 x .378 at 2760 out of that barrel length with zero signs of pressure (H5010). I was a little disappointed until I ran the ballistics on that load and had just over 2000 ft# (recommended energy threshold for elk) at 1000 yds, and almost 1000 ft# (whitetails) at one mile. Since you're going to be single loading, you've got a lot of flexibility in setting OAL, and with a factory dimension reamer, you might not have to run a throater in at all. If you decided on the Wby chamber, you definitely don't need a throater! I'm not smart enough to know what all could go wrong if you sunk a .338 RUM reamer to chamber a .338/.300, but every instinct I have tells me not to do it!
The big .338's are my favorite caliber, with the .340 Wby being the lower limit.
Texas State Rifle Association Life Member
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A big fast bullet will beat a little fast bullet every time
Last edited by specweldtom; 08-15-2007 at 01:10 PM.