In the past, I have mounted scopes and just leveled the crosshairs holding the rifle offhand. I do a pretty good job as will be seen below. Typically, I zero my deer hunting rifles 2" - 2.25" high at 100 yards which is dead on around 225 and 6" low at 300 (.280 Rem 140 BT). I have used it out to 325 yards and feel comfortable shooting a bit farther than that using holdover. I shoot highpower and feel very confident about 1st round hits to at least 600 yards with adjstible turrets so I decided to rig my rifle better for the task. I received a 3.5-10x40 Leupold CDS with a plex crosshair as a gift and sent it back to Leupold to install a CDS windage turret. After reading about how some of you guys check the installation of your scopes, I tried the following experiment: I used a blank piece of paper at 100 yards. Using a level, I drew a vertical line 18" long. I thin drew a horizontal line to form an upside down "T". I shot my rifle on my 100 yard zero (needed a bit windage to get it centered). To save a bit of time and most importantly barrel heat, when it looked centered, I added 15 MOA and fired 2 more shots. As you can see from the attached picture, the center of my 100 yard group was about .3" left of centerline and the +15 MOA group was on the centerline. If you drew a parallel vertical line through the lower group, the center of the upper group is .2" from the parallel line. Here are my questions: 1) Is this deviation within acceptable tolerances for shooting out to 600 yards? Or should I try to turn the scope in the rings to correct it? 2) I have been experiencing an odd phenomenon. When My scope is zeroed for 100 yards, I get some horizontal (still well under MOA). When I add elevation 9 - 15 MOA, I always end up with all shots touching. One day I even did this alternating shots between zero and +9 MOA. Weird. Anyone care to comment? Rifle is a McMillan Signature. 24" #3.5 barrel (Rem mag profile) with Burris Weaver style mounts and Burris low 1" Zee rings. Any comments appreciated. Dan PS Those are two 2 shot groups with a 1/4 MOA right wind correction between them.