I purchased a 2.5-10x44 rifle scope for my CVA Accura V2 muzzleloader this year. I had my favorite scope (4-16x50 Viper HS LR) on the muzzleloader last year but I moved that scope over to my 28 Nosler X-Bolt. After many trips to the range, I had just found that 300 yards was the extended range my muzzleloader, bullets and my abilities to ethically shoot were. With that knowledge, I felt a smaller scope was in order so I went with this 2.5-10x44 HS scope.
My only hunt with a muzzleloader this year was for elk here in Utah. After a number of trips to the range in preparation for the hunt, I kept getting poor accuracy with 300 Gr Aerolite bullets that have always shot really accurately for me in the past. I also noticed that vertically an adjustment of 2.5 inches up would change the point of impact by 5-6 inches at 100 yards. What was up with that? Then on two occasions, I noticed that when I went back to the range my zero had been lost and I would have to adjust the scope again. What the heck?!? None of my other Vortex scopes had ever acted this way.
After a couple of phone calls and emails with Vortex they very nicely let me know that they felt I had over torqued my rings and I was convinced that this couldn't be the problem. I use a Wheeler torque driver and originally torqued the screws to 18-inch pounds. After talking with Vortex I cleaned the Loctite off the screws and torqued them to 16-inch pounds and back to the range I went. And once again the scope was changing the point of impact by double the amount I was adjusting. Ha, I was right or was I???
So back I went to Vortex convinced as ever that there had to be a problem with the scope. I had lost all confidence in the scope and wanted another one. It was at this point that I was just about ready to send it in when I had a great conversation with Adam at Vortex. Adam explained how the scope worked and why overly tightened rings could cause issues exactly like I was experiencing. Thank you, Adam! Being a DIY kind of guy I wanted to figure out what was going on myself to make extra sure that is was or wasn't the scope before going to the trouble of sending it back to Vortex.
In discussing how the scope operates with Adam I learned that when a scopes rings get torqued too high it creates extra tension that makes any adjustment change the point of impact by more than it is supposed to, that is until over time the scope settles back to where it was "really" adjusted too. As I thought about it this was exactly what was happening to me. Adjusting the scope would move the point of impact twice as far as it was supposed to change. When I would go back to the range another day my zero would be off by half of the distance from what I adjusted the time before. And because it was in the process of settling to the right position my groups would be less than stellar.
So what was causing the extra tension on the scope tube? I figured the first thing that I would do would be to try some different rings. Before I ordered some rings I decided to give the set up a really good inspection. Had I messed up placing the wrong corresponding MOA shims in my Burris Signature Zee rings or something else? So before I pulled the scope off I looked it all over closely and I found what I believed could be the problem.
Because this scope was on a slow shooting muzzleloader I wanted to tip the scope down 10 MOA in the front to keep the reticle centered closer to the center of adjustment. So, I set the front rings with a minus 10 MOA on the bottom and a plus 10 MOA plastic insert on the top and on the back ring just two "0" MOA plastic inserts. In this manner, I would tip the front of the scope down for a 10 MOA incline. What I couldn't see was because of the 10 MOA incline the self-aligning plastic insert on the bottom rear ring was sticking out from the ring just ever so slightly and it was putting pressure on the tapered incline of the rear of the scope tube. This happened because I had set the scope as far forward as possible. When mounting the scope originally I was looking down from the top and could see that I had clearance from the ring to the taper of the back of the scope tube but I didn't realize that the insert was sticking out on the bottom and was applying pressure to the taper of the scope tube.
So, was this the problem? Yes, it sure was. I mounted the scope an 1/8th of an inch farther back giving it plenty of clearance and headed back to the range. The scope is now tracking perfectly and my accuracy has returned. Awesome! Confidence restored and I didn't have to look like a novice shooter to the Vortex team by sending it back to find nothing wrong with it. :)
Vortex, thank you for your patience, help and for making great products!