GoodGrouper,
I would not think there would be any action work at all needed to convert the Browning in 300 Win Mag to either of the two rounds you are looking at.
As far as velocities go, I tend to be a little conservative and as such I would say out of a 26" barrelI would say using a conventional cup jacketed bullet or Ballistic Tip, you should be able to crowd 3100 fps pretty hard and in a 27" pipe I would feel it would get a little more.
This is all dependent on your barrel though but with a custom throat, I see no reason why you could not reach this level. The 300 Win Mag can do it with factory throats!
Between the two, I have only had experience with the 30-338 and was impressed with its performacne. I devloped a load for a customer in a custom rifle he had but he was using the 200 gr Parition and if I remember correctly, it took exactly 9 rounds of testing to get a load that cut 1/2" groups at 100 yards for three shots. Velocity was inthe 2900 fps range and I used Rl-22 I believe.
Personally, I would choose the 30-338 over the Norma every time simply from a case forming standpoint and price of brass. You can use any 7mm to 338 standard length belted magnum case to cold form the 30-338 and it needs no real fireforming.
I used virgin 7mm Rem Mag brass with my customers loads and they shot extremely well. Sure they will be more consistant with fireformed ammo but it is plenty accurate to load and hunt with.
The round seems as easy to load for as the 338 Win Mag which I believe is one of th easiest rounds out there to load for in a quality rifle, generally shoot most bullet weights very well.
Hope this helps a little!
Have a good one and let us know what you decide.
Good shooting!!!
Kirby Allen