I wouldn't take no .22 center fire for a sheep, you gotta be nuts!! Sheep are some of the toughest critters pound for pound, theres about 350-400 lbs of solid muscle on a big Ram. I wouldn't even use my beloved 25-06. I would say the minimum I would take is a .270 win w/140g AB or something similar. Sheep are known for being tough and any 7mm, 300, 338 WM is not out of place. YOu want to be able to anchor them on spot because you dont want them running off in that kinda terrain, not to mention it might be a trophy of a lifetime.
Not saying the .22 cal is the best choice, but it will do the job. I've seen more than several wyoming elk fall to the .22x.243 at ranges up 800yds. Like I said its not the best tool, but it will get the job done with precise bullet placement, an experienced shooter, and the proper bullet selection. Also I agree that the WSM's would be hard to beat in that situation.
If I were looking to build as light of a rifle as possible and still have legit consistant 500 yard reach, I would probably go with a 280 AI. The reason would mainly be that the 7mm offers a great selection of bullets. My first choices would be the 169.5 gr ULD RBBT Wildcat or the 160 gr Accubond.
These are more then you need for sheep but in sheep country it is often windy. Alot of times VERY windy with alot of updrafts, down drafts and multidirectional winds. The high BC bullets would help greatly in these conditions yet still they are not so heavy that recoil would be severe.
The 280 AI can be housed in a Rem 700 which is lighter then most custom receivers of the same design. I would go with a carbon fiber Manner stock, two piece Burris DD bases and DD signature rings with a lightweight Leupold scope in the saddles.
More then likely I would use a DE brake as well. barrel length would be 24" and barrel contour in the #2 to #3 Lilja range, 1-9 twist 6 groove.
The 280 AI will do pretty much anything the 7mm WSM will do and feed MUCH better as well then the stubby fat WSM. Most of the 280AIs I have built for customers come suprisingly close to matching the 7mm Rem Mag in 24" barrels.
For a bit more weight though, I would also lean toward the same basic rifle but with a 26" barrel in 270 AM loaded with the 169.5 gr ULD RBBT to 3350 fps. 500 yards would be a chip shot and terminal energy would be far greater then most other chamberings in such a light weight rifle.
Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.