Sir Robin - Thank for the question. I agree with you. If I had to chose a caliber for a beanfield rifle down here in the South, I would not go with my beloved 308 for my first choice. You are right in saying a 270 or 280 would be a better choice. Because a beanfield field would be more than a 200 yards and maybe out to as much as 600 yds. I have a 7mm Rem Mag that has 10 twist that shoot dime groups at 200 yds using 140 gns bullets. 270 WSM or 270 Wea would be good choices too....even 25-06 Rem or 257 Wea would be better.
I know a 308 is very lethal way past 500 yards but after 200 to 250 yards the bullet drop becomes an issue. At 500 yds a 165 gn bullet will drop somewhere around 50 inches if sighted in at 200 yards and most than that if sighted in at 100 yds. I sight my 308, 7mm-08, 243's size cases in at 100 yds, the 30-06 size cases including the 270 and 280 at 200 yards and my magnums size cases at 300 yards. But that is just something I have standardized on over the years. And you are right if conditions are right with no wind, no cold front blowing in, Humidity is pretty low and the barometric press is stable then yes I would maybe take a 300 yd shot, but only if Condition is right.
My 308 size cases rifles are set up with a short heavy barrel 20", 1.5-6X or 2-7X scopes for thick cover, and if of those 1 in a 100 shots come up with a big buck standing out 200 to 250 all you have to do is remember lucky 7. Adjust you scope 7 clicks up with a 308 and you will be dead on at 200 if not you will be darn close.
OK, now I am going to go through my thought process on setting up a beanfield gun. You are going to need more that a good rifle and scope. You will need a good spotter scope, a 1200 yard rangefinder and some very good 10X binoculars. My rangefinder is Lecia, my spotter is Swarovski and my binoculars are either Zeiss or Swarovski. My scope would be Zeiss Conquest with Rapid Z1000. My bases and rings are Ken Farrell or Badger Ordinance - Steel of course.
My caliber of choice would be a 270 Wea, has been for years, now 270 WSM or 7mm Rem Mag. using 130 of 140 Berger VLD bullet. My rifle would be a custom bolt action in one of these calibers with a 26" or 27" Shilen or Krieger, Bartlin barrels, with 10 twist. Jewell trigger, Stiller action...for starters or for fun get you a Savage 12F Class with it's 30 barrel! that would be some fun...Then I woke up...
And of course practice at those distances - a lot! But when you get into the woods hunting, you never know when or where a monster buck will step out. Sure a 308 will do the job, easily but for a beanfield gun, you want one that is very flat shooting so it doesn't drop 50" at 500 yds...
Shooting long distances is not very hard but you understand to do so you have to get to know your round and you cannot change it. Even as much as going from a 130 to 140 gn will change dramatically down at 400 yards...and the most importand is to practice and shoot a lot.....
Starting middle of next month, I will start shooting for Safari 2011...shooting from 200 yds to 600 yds using a 300 WSM and 300 Win Mag....I have 6 boxes of 180 Gn Barnes TSX ready to reload actually starting today....
PS - I have a rare Savage 30-06 24" Heavy Barrel...I know it will shoot great and I am still working on that magic load, now that would be a good beanfield rifle too! As you suggested...