Precision Scope Mounting for the Working Rifle.
By Jim See of Elite Accuracy
Everybody seems to be an expert when it comes to putting stuff together but a novice when it comes to diagnosing zero shifts, and accuracy problems with their rifles. I decided long ago I was going to make my ability to diagnose problems much easier by applying some principals I learned from some of the best Rifle Builders and Shooters in the country.
It’s all about Stress, and Eliminating It.
So let’s talk about the connection of Rifle to Optic. Today we have some of the heaviest optics ever used by precision rifleman. Optics north of 2 lbs. is more common now than ever before. With the increased weight of optics, our mounting system has to be that much more robust to keep the rifle and optic in perfect harmony under heavy recoil and the rough handling of today’s tactical style of rifle matches.
While attending a gunsmithing class under the bench rest hall of famer, Speedy Gonzales, back in 2008 I learned an interesting way to secure optic to rings for a 100% stress free mount while getting as near to perfect contact as possible.
Now you might think I am talking about ring lapping but you would be wrong. The issue with ring lapping is your lapping bar changes dimensions just like the rings do, as the abrasive compound used affects both ring and bar. But since you continue to use the same lapping bar on multiple rings the wear on the bar accumulates, until the lapping process is just that; a process, that creates no consistent results.
Well, that’s easy to understand, the next thing you will hear from the nay-sayers is that; “today’s premium rings are machined to such high tolerances that you should do nothing, just bolt them to the rail and go.” The problem with that line of thinking is nothing is perfect in mass production, and there may very well be a tolerance stack from the; action, to picatinny rail, to rings, to scope tube diameter. When was the last time you had and action, rail and rings all made by the same manufacturer who would have at least a little control over tolerance stacking? My guess is never.
So what is the best way to secure a perfect fit? To start with let’s look at some rifle actions. Some custom actions have integral rails machined from the same block of steel as the action and are typically as straight and level as can be achieved. Second we have custom actions with pinned and bolted on rails which can be nearly perfect but sometimes are not. Basically due to the machining practice of fixturing a long skinny work piece that may deflect during machining. An example of that is in the following picture. This is a custom action and rail fitted together with a precision ground parallel placed on top of the rail. There was some arch in the rail fitment which can be seen by the small gap in the back of the rail. The rail has a slight arch to it, which would lead to misaligned rings no matter how well machined those rings are.
Lastly we have factory actions with aftermarket rails, made in factories thousands of miles apart. The fit on these can be downright disturbing and is often times the reason you hear people refer to “bedding the rail” many times you can create; a cup, a dish or even a twist in the rail when bolted directly to the receiver. So yes a proper “stress free epoxy bedding” of the rail to receiver is a great place to start.
Epoxy Bedding the Optic in the Rings.
Now let’s get to the meat of this article. Regardless of our action/rail status let’s assume we use the best available practice for mounting the rail to action. This will get us as close as we humanly can to a flat straight plane to give our rings a good base to align themselves with.
We now can begin the quick and easy process of Epoxy Bedding our scope to the rings for a 100% stress free mount. The next picture is where we start. The ring bottoms are properly spaced on the rail and torqued down to the manufacturer’s specifications. We then want to set the scope in the rings and gently slide it back in forth with no binding. This will tell us that there is clearance between the scope and rings for the epoxy to fill. You will notice the aluminum to aluminum surfaces are slippery, that will change with a dry epoxy “gasket” when we are finished with this process.
Now the caveat is; if the scope binds in the rings, we have a misalignment of the rings, likely due to poor manufacturing or from a tolerance stack, or twisted rail. The Solution is to now lap the rings to provide clearance so the epoxy bed can do its job. Once the rings are lapped for clearance we can continue.
The use of the proper tools; like the digital Fat Wrench from Wheeler Engineering and the Wheeler scope leveling kit are great aids in the proper mounting of our optics, they insure a level mount and proper torque settings of all fasteners, which is critical to the functional operation of the optic.
Our next step is to apply a release agent to our optic so that we don’t permanently glue it in the rings. For this I like aerosol release agents, they go on wet and dry in seconds to a very thin film. Typically any aerosol release agent used for bedding actions to stocks works well for this. The next picture shows a wet release agent flashing off just after spraying.
Next we need to choose a suitable epoxy for the job. Almost any 2 part epoxy will work but I like JB Kwik Weld. It will give you about 5 minutes of working time and will cure hard enough in about 20 minutes that you can begin the clean-up process as I will outline soon. Make sure your rings are cleaned and degreased so the epoxy adheres to the rings permanently.
Set the scope aside and properly mix your JB Kwik Weld, you don’t want to waste your time once it’s mixed, because you are in a diminishing working window as the epoxy begins the hardening process.
I use the stem of a wooden q-tip to roll some of the epoxy up on to the stem and then roll it onto the ring in a thin layer so it looks like the next picture.
Once the epoxy is laid down take your optic and orientate it as it would sit in the rings during mounting. Set it in the epoxy bed and hold it there while preventing it from sliding around. Then take your ring caps and screws and install them to hold the scope in position on the rings. This part is critical to the proper stress free mounting,
DO NOT TORQUE DOWN THE RING CAP SCREWS!
We want to just snug them up enough to hold the scope in position and not induce any stress on the optic. The goal here is a layer of bedding that makes a perfect cylinder to match you optic from ring to ring. I typically use the long tail of the wrench, between my index finger and thumb, and just roll the screws snug that way as shown in the next picture. Do not grab the leg of the wrench and put undue pressure on the screws.
Once the ring caps are snugged up but not torqued you will see a small amount of squeeze out on the ring. If you overdid the epoxy you might have a big mess, the right amount should look like this next photo. Do not try and clean up the wet epoxy now. Let it harden, clean-up is much easier that way.
I typically give JB Kwik Weld about 20-25 minutes to cure then I am ready to remove the optic and clean up the small ribbon of squeezed out epoxy. The optic should easily pull out of the epoxy bed and the epoxy should remain on the rings. The next picture is of that description.
Now simply take a sharp exacta knife and trip the ribbon of squeeze out away from the ring. This is best accomplished by coming in at a 45 degree angle with the blade and letting the ring itself guide your cutting path. The finished product will look like this. Remember to wipe off the optic of any residual release agent and clean or dust off your parts.
What you have just accomplished is a one to one fit 100% stress free and to the most exacting tolerances.
With the clean-up complete we can now go on to mounting our optic, using our Wheeler leveling kit and the best practices to accomplish the task. Use the proper torque setting on the ring cap screws to ensure you do not exceed the scope manufactures torque values.
One thing you will notice when setting the scope back into the rings is that the slipperiness of ring to tube is gone. That epoxy gasket is a perfect fit and an anti-slip coating which will allow your scope to stay in place with less torque value. This process works especially well on; light, high recoiling rifles, which are prone to scope slip under recoil.
From my personal view I can tell you over shooting rifle competitions since 2008 at the highest level of State and National competition, and hunting around North America, I have never had a loss of zero or scope shift due to my mounting system. The fact is; this is simple and easy peace of mind, that what you have accomplished is going to keep you immune from potential scope mounting zero shifts, from the hard knocks and rough handling in field conditions.
About the Author
Jim See has been building rifles professionally since 2007 when he opened “Center Shot Rifles” in Pittsville WI. He later moved to Oklahoma and spent 2 years with Surgeon Rifles. A family moved has Jim in Decorah Iowa since 2015 where he builds rifles and offers Competition Training classes for rifle enthusiast across the country, under his new company Elite Accuracy LLC. Jim continues to shoot in NRL and PRS matches where he has finished in the top 25 nationally for 7 consecutive years. www.eliteaccuracy.com