Both Pictinney and Leupold are screwed into the action via pre-drilled mounting holes, so I'm confused with your description. Pictinny allows the use of a much greater variety of rings where the Leupold bases are dedicated to Leupold rings only. I use some of each on different guns. Generally, a one piece base such as the Pictinney (or Weaver type) reduces the chances of the rings being misaligned which can cause the scope to not sit in the rings as well as they should. I prefer a one piece base over a two piece set up if given the choice. If I have to use a two piece base I usually opt for a Leupold if they have a set that fits that particular gun. Both will hold zero fairly well, and both have been used on the hardest kicking magnum rifles out there with no problems. If they are mounted correctly they will both function very well. Unfortunately, a lot of inexperienced "gunsmiths" don't know how to mount a scope correctly and don't know what problems to look for. Over torgueing is very common as well as under torgueing. Also, some systems don't lend themselves very well to being able to move the scope fore or aft to accomodate eye relief and the user ends up with the scope not quite in the right position. FWIW, I've probably mounted a few hundred scopes over the last fifty plus years. Do you have something specific in mind?