Question: I've heard that recoil will cause a scope to move in the rings. I guess I have to tighten the mounting screws really tight. Is that right? Below is your answer...
Farmer Tight: Wrong or Right?
There is a lot of misinformation floating around about how to mount a scope. Much of it should be titled “How to Mount and Ruin Your Scope.” Have you ever seen a scope that has “ring marks” on it? Have you ever heard someone complain that their scope was “defective out of the box”? Have you ever heard someone complain that their new scope can’t seem to hold a zero? These are just a sampling of what happens when a scope is mounted incorrectly.
Mounting a scope seems like a pretty simple operation. It is; if done correctly. Before we get to some of the correct procedures, let’s take a look at the modern scope. The average scope is made from an aluminum tube which is fairly durable but it’s still an aluminum tube. Inside the tube is what is called the “erector tube” which is precision made to move inside of the exterior tube. The erector tube moves side-to-side and fore and aft inside the exterior tube of variable scopes. These movements make possible the changing of magnification and adjustments for point-of-impact. As you can imagine, you wouldn’t want to do anything to the exterior tube that might restrict the erector tube movement. Correctly mount your scope and you won’t affect the movement of the erector tube and your scope will perform as desired.
When you hunt, you want to have the confidence that your rifle and scope will perform accurately at that precise moment you squeeze the trigger on your trophy animal. Confidence means you are not second guessing the performance of your rifle or scope. Wind or distance to the target maybe, but that’s for another article.
Now for the most common problem that causes most of the complaints described earlier. A recent article in American Rifleman used a term that is very descriptive of the problem; the author used the term “farmer tight.” In a nut shell, farmer tight means to tighten as much as you can. Well, as you can imagine, you can tighten the typical 6-48 or even an 8-40 screw used with scope rings so much that the screw becomes ruined in the process and that is why the mounts eventually come loose. But that’s not the worst part. The worst part is the damage, both visible and invisible, that is done to the scope; in particular, the scope tube. It is amazing how many people, even big named gunsmith shops, over tighten scope ring screws “just to make sure it doesn’t move during recoil.”
OK then, how much should you tighten the screws? Answer, lot less than most folks realize. More specifically, 15 to 20 inch pounds for the rings depending on the manufacturer and type of rings. That’s not much. In fact, you can loosen a Torx-head screw tighten to only 15 inch pounds using just your thumb and the first two fingers holding a typical screwdriver. That’s it. Don’t worry about the scope moving or coming loose. It won’t. The same holds true for the screws on the bases. Even the mounts by some manufacturers on Picatinny rail bases where ½” nuts are used call for only 65 inch pounds. Much less than that farmer tight mentioned earlier. Others using 8-40 screws call for tightening their bases with 35 inch pounds; nowhere near farmer tight. The bottom line here is to follow manufacturer’s recommendations for your rings and base…never tighten the screws “just a little bit more to make sure.”