I picked up my Colt LE6944 yesterday. It came with three rail covers. I tried to install them by sliding them on they wouldn't go past about half of an inch. Then I tried to just put them on from one side to the other and found that they're not flexible enough. So, what's the trick to getting these rail covers on? Seems like it should be easy, but I don't want to mangle anything. They look like the ones below except that they're black.