Anyone thinking that the grease they just applied to their mainspring means they've tuned their gun is delirious. The grease is there to lubricate the mainspring, which is in contact with both the spring guide and the inside diameter of the piston. A tuned gun has much better fitting guide set which does keep the spring straighter, and THIS is what reduces spring vibration. The spring tar is there to supply lubricant to the snugly fitted guide. Tar-like greases are used because they are much better at staying put when the spring coils are freely released during firing. Loose greases and oils will be flung around all over the internals of the gun and migrate where they are not wanted.