Presented by Crimson Trace
I’ve had occasion to mount quite a few scopes in my time. I don’t want to brag, but I’d wager I’ve installed just as many scopes as that kid at your local Cabela’s.
Unlike that kid at Cabela’s, however, I always try to install scopes the right way. It probably goes without saying, but it’s tough to hit much if your scope is loose, crooked, or otherwise impaired. Proper scope installation isn’t difficult, but it helps to have a few special tools, and it often takes a little patience.
Here’s the method I’ve developed.
Step 1: The Tools You Need (Sort Of)
I hate how-to articles that begin by recommending tools I don’t have. So, I’ll just say that having an inch-pound torque wrench and a scope-leveling device is extremely convenient, but not essential. You can estimate both torque weight and reticle level, but tools like the Wheeler F.A.T. Wrench and Professional Reticle Leveling System provide a little peace of mind.
You’ll also want some kind of sled or gun vice. I use a Caldwell Lead Sled, but there are a wide variety of products that will do the job.
Step 2: The Gear
Scope and ring selection isn’t really part of the scope mounting process, but there are a few things beginners might want to know.
First, be sure to select scope rings that match the diameter of your scope. The majority of scopes use either a 1-inch or a 30-millimeter tube, and you can usually find that info on the box. If you don’t have the box anymore, a set of calipers will give you the correct measurements (FYI: one inch is smaller than 30mm).
Also, don’t forget to consider ring height. Accepted wisdom calls for rings that keep the scope as close to the bore of the gun as possible (so, as low as possible). This is a good rule of thumb, but also consider the positions from which you’ll likely be shooting. In the prone position, a scope mounted using tall rings can be uncomfortable to use, but the opposite can be true in the standing position.
I don’t often take shots from the prone position in the piney woods of East Texas, so I opted for the higher set of Wheeler rings.
Step 3: Secure the Gun
With those preliminaries out of the way, it’s time to get down to business. Start by unloading the rifle and securing it in a vice or sled. Don’t skip this step. You won’t be able to mount the scope properly if you have to use one hand to keep the gun upright (or, heaven forbid, mount the scope while the rifle is on its side).
Step 4: Secure the Ring Bases
When you select your rings, be sure that they will attach to whatever kind of scope rails are affixed to your rifle. Picatinny rails are the most common (what you find on most AR-15’s), but there are also dovetail and Weaver rails. If you aren’t sure which yours are, you can try to look it up or purchase rings for both and return the set that doesn’t work.
Your scope rings should come with torque specifications for both the base (the part that mounts to the rail) and the rings (the parts that go around the scope body). Wheeler recommends 40-50 inch-pounds for their scope ring bases, which translates to one firm pull (the technical term) with a ratchet.
Step 5: Determine Eye Relief
“Eye relief” is the distance your eye must be from the ocular lens of the scope to achieve a full field of view. If your scope is mounted too far forward or backward, you’ll see a partial black ring at the edges of the scope when you look through it.
To determine proper eye relief, set the scope in the bottom half of the rings and hold the rifle in the position you’re most likely to use in the field (to make sure the scope doesn’t fall out, you can also loosely attach the top half of the rings). You should put the scope on its highest power. Shoulder the rifle as you would while taking a shot and look through the scope. Move the scope forward and backward in the rings until you see a complete field of view without any black around the edges.
The Crimson Trace Brushline Pro has a surprisingly forgiving eye relief range, so I didn’t have much trouble finding a good place to mount the scope. Once you have the scope where you want it, either mark the tube with a pencil or keep it in the same position while you secure it to the vice or sled.
Step 6: Level the Reticle
This is the most tedious step, but there’s no way around it. Ensuring the reticle is level with the bore of the gun will keep shots on target if you shoot beyond the zero range. The Crimson Trace Brushline Pro comes with handy bullet drop compensation markings for shooting at longer ranges, but those marks won’t do you much good if your reticle is crooked.
There are a wide variety of products and techniques that can help you ensure a level reticle. I covered three inexpensive options here, but my go-to system has always been the Wheeler Professional Leveling System.
Users start by leveling the rifle, and they can maintain that position using a level that attaches to the barrel. Then, a separate, magnetized level can be attached to the top turret of the scope to ensure that scope and rifle are both on the same plane.
You should keep two additional things in mind. First, sometimes a scope’s top turret isn’t quite aligned with the reticle. In that case, you’ll have to use a plumb line to level the reticle rather than a bubble level on the top turret.
Second, be sure that the scope doesn’t turn as you tighten the scope ring screws. There are a few ways to mitigate this. Some people recommend using shims or feeler gauges between the scope and the rail, though I’ve never tried this. I just tighten the screws very slowly in a star pattern while keeping an eye on the level. If it starts to cant to one side, I loosen the screws and start over. It’s a tedious process, but totally necessary for accurate long-range shooting.
Step 7: Tighten the Ring Screws
Crimson Trace (along with most scope companies) recommends using between 15-18 inch-pounds of torque on the scope rings. This isn’t very much. If you don’t have a torque wrench, 15-18 inch-pounds is about as much torque as you can apply while gripping the short end of an Allen wrench.
There’s some debate about using non-permanent thread locker (blue Loctite) to secure scope rings. Vortex recommends against thread locker because it can throw off a torque wrench. Wheeler told me it’s not harmful but also not necessary, so I decided against it. I’ve used it in the past (and even recommended it), but I’ll go with the experts in this case.
Once you’ve tightened each screw, tighten each screw again. Oftentimes, I find that I’ve either missed a screw or one has become looser when I tightened the others.
Once you’ve torqued down your scope rings, you’re good to go. It’s not a bad idea to periodically check the base and ring screws for tightness, but if you’ve mounted the scope properly and haven’t dropped the rifle, you shouldn’t have anything to worry about.