It always amazes me that such undemanding lubrication environments such as gun lubrication can polarise so many different opinions! My tuppenceworth FWIW is that with a little thought, it isn't exactly rocket science and that it's a shear action, high pressure environment so boundary lubrication rather than hydrodynamic (ie oil!) is needed, and must be corrosion resistant, not readily oxidise even over prolonged periods, provide good high pressure and shear resistance, and be safe to use. There may be some oils, thinly used such as automatic transmission fluids that'll do the job fine but these can often be toxic so best avoided.
My recommendation (and what was recommended to me by a lubrication "expert") was food safe, food industry aluminium based food machinery white grease compounds. These exhibit exactly the qualities needed for a rifle bolt and bolt receiver and only a thin coating is needed. As for all the "abrasive compound" comments with grease...poppycock if you regularly clean your rifle and ensure there's no build up. Remember that even with abrasive powder residues, they will not rapidly break through and remove the boundary grease layers on metal surfaces when viewed microscopically (or so I am assured), especially when most of us wont be stringing dozens of shots off at every outing. If target shooting, one can always remove the bolt after some strung out shooting, wipe down and thinly re-grease. You probably take all your kit to the range anyway. For those who treat their rifles like walking stocks, to be used and chucked in the cupboard after every outing like any other "tool", well don't complain when things start corroding or wearing prematurely. A rifle is not just "a tool", it is a precision instrument and really does need to be treated with appropriate care. That care applies as much to the cleaning of the rifle as anything else. But keeping a rifle in fine fettle is not that demanding.
Here's a relatively cheap example available off Ebay:
http://www.ebay.co.uk/itm/FOOD-GRAD...791376?hash=item3d04846850:g:2icAAOSwIBBUayYG
Remember, that's for a whopping 400g,more than you'll need in years and it's basically the same as a lot of these hyped up "gun specific" white greases which cost considerably more...wake up and smell the coffee! Few gun lubrication products have ever been specifically developed purely for firearms use, the wheel was already invented elsewhere. Most are simply aluminium based grease compounds like this one. Its the same stuff used in kenwood chef gearboxes. We have one which is 50 years old, used regularly and still going strong.
Even better, and cheaper:
FINE GRADE SYNTHETIC WHITE GREASE WITH PTFE 50 GRAM TIN FOOD SAFE GREASE | eBay
Think about it: food processing industry is often in humid and corrosive environments, where excellent corrosion and chemical attack resistance is needed, where good boundary layer lubrication for high wear parts like gearbox cogs and other high pressure applications is needed and which has good migration properties and must be non-toxic.
When I buy a rifle, one of the first things I do is to strip it down, clean all the parts (remember the proof houses leave things like barrels with all sorts of crap in them), remove surface residues of metal parts using meths and a rag/Q-bud, then apply a thin coating of white food safe grease to bolt receivers and bolt surfaces, just a thin coat. After each outing, the rifle is cleaned and re-lubed. It's not hard.