Re: .270 wsm max effictive range??
To answer the original question, your max effective range is determined by the velocity, BC and expansion characterisitics of your bullet and it can vary maybe a couple of hundred yards in the same rifle depending on the bullet and load you are using. An extreme example of this would be, let's say, a 300 WSM loaded with H4350 and 180 AB's going 3000 fps vs RL17 pushing GS 177's @ 3300 fps.
The 180 AB's have a listed BC of .507 and expansion velocity of 1800 fps.
The GS 177's have a listed BC of .638 and an expansion velocity of 1600 fps and are going 300 fps faster.
At 5000' elevation, the 180 AB reaches it's expansion velocity (my definition of max effective range) of 1800 fps @ 850 yds. The GS 177 reaches it's expansion velocity of 1600 fps @ over 1500 yds. Big diff eh?
On the next question of rechambering to a 300 WSM... I would... IMO it's a better all around hunting cartridge and will give you more range, more punch and longer barrel life.