Rings and Base
By Ian Kenney
It is the rings and base that allow the attachment of the sighting system to the rifle and turn it into an integrated precision rifle system. This article will take a look at some of the materials and types of rings and bases common in the tactical shooting community. My hope is that at the end of this article you will have a better understanding of how the combination of these two components allow the scope to have enough internal travel to hit those really long shots.
Scope Rings
Scope rings come in an assortment of shapes, heights, and diameters to accommodate the dizzying array of scopes on the market. There are many companies that make scope rings but only a few are truly suited to be used in tactical environments. Tactical scope rings are often built to exacting tolerances and designed to attach directly to Picatinny/MIL-STD-1913 rails by means of a cross lug and rail grabber set up. This can allow the scope to be taken off of the base and then put back into the same rail slot with a minimal shift in zero.
Design and Function
A majority of the tactical rings on the market are made out of either steel or aluminum, with some brands even making them out of titanium. Steel rings were once all the rage for the tactical market because they were extremely durable but came at the cost of extra weight. Aluminum and titanium rings solved the weight issues but also maintained the necessary strength and durability for tactical rifles. The typical scope ring is a two-piece design with a base that attaches to the Picatinny rail and a ring cap that goes on top and is held in place by four or six screws. The base of the ring is secured to the base on the rifle by means of a rail grabber/foot that is torqued to about 65 inch pounds in most cases. The base is prevented from going forwards or backwards under recoil by a lug in the bottom of the ring. The ring cap works by clamping around the scope with about 18 inch pounds of torque per screw to prevent the scope from shifting under the rifle’s recoil impulses and other forms of shock. Depending on the manufacturer, the rings can be made in matched pairs or line bored to ensure the rings stay as concentric as possible when mounted onto the base. This level of precision and machining can be expensive compared to other methods of production however, it can reduce or eliminate the need for lapping. This also reduces the chances of damaging the scope's main tube through twisting or bending.
Diameter and Ring Height
The diameter of the rings will depend on the particular scope but it should correspond to the diameter of the scope’s main tube in order to work properly. Tactical scope rings are typically made for scopes with a main tube diameter of 1”, 30mm, 34mm, and 35mm. Some companies make ring reducers available that can convert a set of rings made for a larger tube diameter to work with a scope that has a small tube diameter. It is worth mentioning that some tube diameters do not allow the shooter to get the scope as low as possible. This is seen in rings designed for 34mm and 35mm main tubes since the lowest ring currently available is .92” for 34mm scopes. This is because there wouldn’t be enough material left to provide sufficient clamping force if it was made to go as low as some 30mm scope rings, it's just the nature of the beast.
Right height is the measurement from the centerline of the scope ring to the top of the scope base on the rifle. This measurement is important when choosing rings because it needs to be high enough so that the objective bell of the scope sufficiently clears the barrel. The optimal ring height will usually depend on the barrel contour and tube diameter but the goal is always to get as low as possible. Scopes that have 30mm main tubes and an objective diameter of around 40mm can get away with a ring height of around .825” and still clear most barrel contours. Step up a 50 or 56mm objective diameter though and the ring height will have to be increased to around .885” – 1.00” in order to provide the proper clearance.
Scope Base
Just like scope rings, scope bases for tactical rifles come in a variety of materials and designs to accommodate the needs of the shooter. Typically the same companies that make tactical scope rings make bases to go along with them so it can be a simple one-stop-shop for the buyer’s mounting needs.
Design and Function
A scope base that is suitable for tactical rifles can be made out of steel, aluminum, or even titanium just like the scope rings I discussed above. The scope base is attached directly to the action by a series of screws, the number of which depend on the type of action. The screws themselves vary somewhat, with most manufacturers using 6-48 screws as the standard thread pitch while others upgrade them to 8-40 screws. Some custom action builders go above and beyond though by machining the action with an integral scope base so that issues with misalignment become a moot point. Scope bases that are suitable for use on tactical rifles will have rail slots that are made to MIL-STD-1913 specifications, otherwise known as Picatinny rails. The name Picatinny comes from the Picatinny Arsenal where the design originated from in the mid-1990’s. Picatinny rails have a series of slots machined into them spaced a certain distance apart and at a certain depth. Weaver bases have similar slots, however their spacing is not standardized and can vary from brand to brand.
In addition to having rail slots that are to MIL-STD-1913 specifications, scope bases can also be machined with some degree of cant to help the riflescope have enough internal elevation to make long range shots. The degree of cant on the base will vary based on the manufacturer but bases for the more popular actions are available with anywhere from 0-45 MOA of cant to accommodate just about any scope out there. The most common degree of cant is 20 MOA since it will allow just about every scope on the market to get a 100 yard zero and have enough internal elevation to go just beyond 1000 yards.
An angled scope base works by canting the scope slightly in relation to the bore axis.
When bore sighting a scope that is optically centered, the crosshairs will be below the point that you see when looking through the bore.
Since the image is inverted inside the scope, the elevation knob will have to be turned in the direction to bring the crosshairs up to the point seen through the bore. For scopes with counterclockwise knobs this means turning it clockwise.
Inside the scope this action pushes the erector downwards inside the tube giving it more room above it, which translates into more internal elevation travel.
The amount of internal travel gained will depend on the amount of cant that the base has, the zero distance, and the scope itself. But lets say that the scope going on the rifle has 65 MOA of total internal travel, that means from center, it has 32.5 MOA in both directions and it is going on a 20 MOA base. After bore sighting and zeroing at 100 yards, the scope can be expected to have about 50 MOA of internal travel available, which is more than enough to reach most target distances.
As the shooter dials in more elevation the erector is pushed up by the erector spring and the reticle appears to go down on the image from the shooter's perspective. This forces the shooter to bring the reticle up on the target, which in turn raises the barrel to compensate for the trajectory of the round.
In The End
That in a nutshell is how the mounting system for a tactical bolt action rifle works to provide more elevation travel for the shooter and keep the scope securely mounted to the rifle. This article didn't cover all of the mounting solutions availabe for a tactical rifle, however the principles in how it all works still applies whether it's a one-piece ring/mount combo or the traditional set up. I hope you came away from this article a little more knowledgeable about these mounting solutions and maybe help make the decision on which one to buy a little easier.