cleaning receiver and screw holes before mounting base question?

[Long Range]

In my instructions to mount the base it says to clean the screw holes and screws with alcohol and or a degreaser.

Why is this exactly? Should you not leave any oil to protect from rust?

In another instructions it says just to clean the receiver and base thoroughly.

Is it OK to leave a little oil on the top of the receiver under the scope base? The reason I ask is I accidently scratched the top of the stainless receiver trying to get those little screw holes out.

To sum it up I guess you don't want any oil on the screws or screw holes, but it is OK to have some oil elsewhere?

Thanks.

 

[damoncali]

They want you to clean the threads because scope bases are held in place by friction generated by the clamping force of the screws, and if you let any oil get in between the base and the receiver, you lose a good amount of that friction.

Ideally, you *want* oil on the threads, because it will give the screws more clamping force to generate the friction. But doing that without letting oil get in between the action and base is difficult, so they just tell you to do it dry. Don't over think it - just clean it up as best you can and tighten it as much as you can without breaking anything.

This is why you see some customs pin the bases in place - that is the proper, but difficult and expensive way to do it. (It also involves putting more holes in the action, which is not something you should do unless you know what you are doing).