I am thinking about getting a Remington 700 in 300 WinMag for long range hunting. In particular, Remington #84164 which has a 26" heavy contour 1:10" twist barrel & a B&C M40 stock. This gun is reasonably priced and I can later add a Manners stock, timney trigger, etc. Probably would get the muzzle machined for a brake right away.
That factory stock
in practical, hunting usage will *likely* be just as good as any of the top-end replacement/aftermarket stocks (especially if you bed/pillar the receiver and free-float the barrel).
How would this rifle do right out of the box?
In general, this rifle should serve you very well, though establishing it's accuracy at distance will certainly need to be absolutely determined.
Remember, these (like all rifles) are subject to the characteristics of the barrel. Remington barrels are hammer-forged which are generally not the most accurate way to make barrels.
It all depends on how well you hope it shoots. A 700P should be good and the LR should be good. If you reload you will probably be happy.
Just as jpd676 says - adjust your accuracy expectations remembering that this is a
mass produced rifle and highest accuracy and tolerances are
absolutely NOT the 1st criteria of the manufacturer.
However, there are some things a normal consumer can do to help improve accuracy in their factory rifle (though ultimately accuracy relies most heavily with the barrel). Things like hand-lapping the recoil lugs of the bolt/receiver face, ensuring the barrel is not touching the stock anywhere and pillar bedding the receiver, bedding the recoil lug and precisely tightening/torqueing the receiver screws. There are other things needed to truly accurize a rifle, but these are reasonably accomplished at home.
I've done these things to my stock, out-of-the-box 1982 production year Rem 700 ADL in 7mm RM. I noticed an immediate improvement in accuracy from 1 1/2"- 3" patterns to around 1" groups depending on the cartridge components. With this rifle I suspect the barrel is the primary limiting factor (and needs to be replaced at this point).