I have an Aztec Emerald 5 - 25 x 50 that I've had for a few years. It's mounted on my HW97. I've had periodic issues with sudden shifts in POI. It's good for an extended period then it will suddenly drift or shift to a different POI. I've looked at other potential problems such as loose scope mounts or rings, shifts in muzzle velocity, etc. Sometimes I think I've found the cause but then it happens again. It is frustrating the heck out of me. I spend all my time testing the scope. I have changed to another cheaper scope I have and have not seen problems with the other scope, but I don't shoot it for a long time because I don't like the coarse reticle and parallax issues.
The image below illustrates a puzzling shift in poi. It's not the worst I've seen but it is a decent illustration. I was changing from shooting JSB 8.44 pellets to the heavy 10.34 grain pellets and re-zeroing the scope. It had been shooting normally for about thirty shots prior to this change. I've numbered the shots I took as I worked on zeroing the scope for the heavier pellet. I made an initial vertical adjustment of about 7 clicks to account for the bigger drop then started shooting. See the image below to track the process. I made one adjustment after the first two shots were right on top of one another. Then there were a lot of rather random seeming shots as I tried to confirm the adjustment. Then suddenly on shot 14 and 15 the POI jumps up a good two MOA. After the second one hit in the same spot I adjusted the scope back down and took a number of more shots to try to confirm that change. I finally got tired of messing with the zero and started shooting individual shots at the remaining targets. I shot at least 25 individual shots, all of which were pretty much on target.
So what would explain that big shift and then a solid consistent zero? The scope rings were torqued to spec. The rifle is shooting a reasonable consistent muzzle velocity. How do I explain a two MOA shift?
The image below illustrates a puzzling shift in poi. It's not the worst I've seen but it is a decent illustration. I was changing from shooting JSB 8.44 pellets to the heavy 10.34 grain pellets and re-zeroing the scope. It had been shooting normally for about thirty shots prior to this change. I've numbered the shots I took as I worked on zeroing the scope for the heavier pellet. I made an initial vertical adjustment of about 7 clicks to account for the bigger drop then started shooting. See the image below to track the process. I made one adjustment after the first two shots were right on top of one another. Then there were a lot of rather random seeming shots as I tried to confirm the adjustment. Then suddenly on shot 14 and 15 the POI jumps up a good two MOA. After the second one hit in the same spot I adjusted the scope back down and took a number of more shots to try to confirm that change. I finally got tired of messing with the zero and started shooting individual shots at the remaining targets. I shot at least 25 individual shots, all of which were pretty much on target.
So what would explain that big shift and then a solid consistent zero? The scope rings were torqued to spec. The rifle is shooting a reasonable consistent muzzle velocity. How do I explain a two MOA shift?