I just had the same issue with a new scope mounted on a new magnum rifle. I won’t mention manufacturer name.
But here goes it:
First of all a little history. I just happen to be a Tool and Die Maker by trade and working to .0001” is a daily occurrence. I’ve been in the trade for close to 26 years and I might have a good idea how to measure things.
Ok. New rifle and I’m breaking in the barrel according to manufacturer’s procedure which requires a 50 shot process with lots of cleaning, so I’m not worried about having the scope dialed in instantly. As I’m reaching 35ish shots I notice my sub MOA gun is not repeating. I’m doing three shot group. Id make elevation and windage corrections before the next group of shots. Proceed to shoot my three rounds. The first shot would be close but no where near sub MOA. By the third shot its way the hell off.
Now I’m getting pissed thinking it’s my rifle. I’m three weeks from hunting season and don’t want to deal with warranty issue. So I take the gun to work. First thing I do is take the gun apart, I mean every down to the roll pins in the bolt. I’m measuring and inspecting everything. It’s all good actually very good to the point I’m impressed with the craftsmanship, very impressed. Which is tough to do with a toolmaker. I clean everything (like medical room clean), and put the gun together. On the way, I do some polishing, edge softening and edge breaking to improve the cycling of a short action magnum, but that’s a different story.
Next up, the scope. First thing I do is clean the scope with denatured alcohol and a soft cloth. Low and behold as I rotate the scope around I see scratch marks the width the rings and it’s only on the bottom half (the reason why I didn’t see it earlier). Houston we have a problem. I measure the 30mm scope it’s right on the ding dong at 1.1811” (30Mm). Next I visually inspect the rings, look fine. On the inspection table I put a ring on the scope and torque it to 16 in/lbs. I grab the 1-2” micrometer and measure parallel with the parting line on the scope, it measure 1.1836”. This tells me the scope is belled out .0025”. Next I measure 90 degrees to the previous measurement. I get 1.1789”, this way the scope is smashed .0022”. Not good. I take the scope rings off. Clean them up and head back the 5-axis CNC. I use it as a CMM (coordinate measuring machine). The rings end up measuring .0023” big. Yep, the companies (rings and scope same manufacturer) top shelf rings measure .0018” larger then the spec which was .0005”. A total of .0023’ above nominal ..... (suggestion buy scope and rings from same manufacturer. If they are not and there’s a problem they’ll point the finger at the other guy when addressing it). So, mechanically what’s happening is there’s two point loads on the scope, the top and bottom.
Now that I know the problem I call the manufacturer tech support. I attempt to explain to him what is happening, why and how I know. I’m not sure he understands. I ask him how we are going to resolve this. He tells me to try torquing it down to 20-21 inch/lbs. and put a piece of tape next to the scope ring which would be an indicator the the scope is moving.
Hunting season is near and now I don’t want to deal with warranty issues, again. So, I mount the scope, torque to the new suggest in/lbs and go one step further. I put loctite on the ring surface. This Significantly increases the coefficient of friction. I head to the range, shoot five times, and have the gun dialed into 1.5 MOA (which realistically is about my accuracy). I haven’t had the problem since.
In December, I’ll be contacting the manufacturer about some quality control issue and hopefully trying out their warranty. It’ll be a fun process which will start with tech support. They won’t be able to address it so I’ll have to work up the chain of people. Fun, fun, fun..
