Perhaps I may be the last to know....I shoot a lot of cast bullet loads in my CF rifles (when I can find primers). I try to keep my rifle scope optics clean and use a brush to do so. However the objective (front lense) will get a film on it from bullet lube. Using a glass cleaner and tissue paper does not work well to remove it; it just smears it up. I recently tried a clean microfiber cloth; I sprayed the glass cleaner on it and carerfully rubbed it on the lense..lightly polishing ---it cleaned it perfectly...sparkling clean. I have found it best to clean the front lense often, to avoid any appreciable buildup of the bullet lube on it.