[MuzzleBlast]

Thinking about building a rifle for precision shooting. Not benchrest, just long-range plinking. What are the pros and cons of these two chamberings?

[Sunray]

Go here. http://www.remington.com/ammo/ballistics/centerfire/comp_ballistics_specific.asp
Depending on what you call long range, the 6.5 x 55 would be much better and you'd have a rifle capable of taking any game up to and including big moose. It uses a heavier bullet too. 180 grain max bullet weight.
The .243 is good up to antelope and other deer sized beasties. Black bear included. Max bullet weight is 115 grains. Berger's. http://www.bergerbullets.com/catalog.htm

[sumpnz]

You might also want to look into 6mm Rem. It shoots the same bullets as .243 Win, but is capable of higher velocities due to the higher case capacity, all else being equal (rifle, bullet weight, etc).

The 6.5mm/.264 chamberings are supposed to be really good for very long range rifle shooting as they have some of the highest ballistic coefficients out there. If you compare sectional density to ballistic coefficient the 6.5mm bullets tend to come out on top againt almost any other common caliber. One big advantage the 6.5 Swede has over even other 6.5mm/.264 cartridges is that it can accept the heaviest, and hence longest (i.e. highest BC) bullets that are available without excessive intrusion into the powder portion of the cartridge.

[scotjute]

My .02 will be a plug for 6.5x55. Been shooting that caliber for about 4 years and really like it. Killed 2 deer with it, 75 and 60 yd. shots.
My shooting has all been limited to under 200 yds. Accuracy has been good and the recoil on the gun is such that I don't wince when shooting. You might check ballistic charts for comparisons.

[jem375]

the 260 Remington would be a good choice also, shoots the same bullet as the 6.5 swede and the 308 based case is widely available............

[BigG]

I would think the 6.5 Swede would have a very tight twist. The 243 and 6mm usually would not stabilize a long bullet even if they were available because of the slower twist. Something to think about.