It's not always necessary to remove all of the best gun lube before applying a new one, especially if the old lube is still providing adequate lubrication. However, if you're switching to a different type of lubricant or if the old lube has become contaminated or deteriorated, it's a good idea to clean the firearm thoroughly and remove all of the old lube before applying the new one. This will ensure that the new lube can effectively protect and lubricate the firearm.