I have no idea who Bruce Gray is. But Clint McKee at Fulton Armory says this: "Oil is bad for semi's. The robust cycling of the action throws the oil all over the place. Grease is better in almost every situation". I agree with him 100%. He goes on..."Tetra oil, or any oil, for that matter, should only be used as a primary lubricant in captivated assemblies, or in assemblies that do not have robust movement. For example, crankcases in engines & motors are sealed, as oil is designed fly around inside them, and thusly lubricate all the moving parts contained within them. Of course, if the crankcase were not sealed, the oil would go everywhere, and drip upon every manner of thing, except that which it was designed to lubricate. The same thing applies to gas guns and recoil operated firearms.
So, use Tetra Oil in any "captivated" assembly (springs, detents, plungers, gears, screws, levers, slides, etc., but only when enclosed in a housing), or in applications where inertial energy will not bleed out its effectiveness. For areas not enclosed, use Tetra Grease, only."
http://www.fulton-armory.com/
Now I am not all that crazy about Tetra Grease any more because I have noticed that it tends to "seperate". They even tell you in the instructions on the side of the tube to squeeze the tube before opening to mix the formula up. That shouldn't need to happen.
So I use either RIG or white lithium grease. Neither one tends to break down.
Everyone has their favorite gunk to put on their gun. I would caution against believeing the internet hype. Often times the stuff in your garage is just as good or better than the expensive stuff labelled as "gun this" or "firearm that".
No, Walther doesn't say to grease the P99. Common sense DOES say that metal-to-metal parts should be greased. And Walther DOES recommend Hoppe's #9 to clean their P99. I have already discovered that is a bad idea on the Walther/S&W PPK with the plastic grips. What's good for one gun isn't necessarily good for all guns.
Dep