Instructions for ordering Bulter Creek flip up covers.(goes for Objective and eyepiece)Measure the outside diameter of the eyepiece(or objective) of the scope.Fit range is .01 under to .025 overthese measurements.That came right out of a Midsouth catalog.You could go directly through Leupold but you'll be paying more for them.I have BC's on almost all my scopes including the Var X11's.

I never had a problem forgetting to open them. If weather permits once I get my rifle pulled up in the stand I open them up.Rainy weather is a different story of course.
Depending how big the #4 is. You can take some Black Electrical tape . Wrap it around the scope then slide the cover over the tape.I've had to do this with a couple of them.I've heard of some putting Silicone sealant on then sliding the cover on. Once it sets it pretty secure.I've never tried the silicone so it's hearsay.. I have lost a couple covers walking through brush. So far I have found them. That's when the Black tape comes in handy if they fit loosely.

Ruger Redhawk