I'm putting a Samson quad rail onto a different upper and I am a total newb to working on AR's. When I pulled it off the first upper there was some oil between it and the barrel and also between the two parts of the rail. Should I reapply oil when I install it on the new upper or should i put it back together dry?
Here's a picture of what I'm talking about.
Here's a picture of what I'm talking about.




















































