Friday, May 28, 2010

Mounting a Scope

Sometimes it seems that nothing is more confusing to a new gun owner, and even some old hats, as installing a scope on a firearm. The sheer number of choices and options in optics alone are enough to write books about, and the ways to actually put the scope on the gun are even more complicated.

This article will attempt to clarify choices and make the novice gun owner’s job in choosing a way to mount a scope easier, while at the same time illuminate the myriad of options for any gun owner.

What You Need to Know (or Find Out)
When you start looking to mount a particular scope on your firearm you need to know certain things before you start shopping for mounting options. To begin with, you’ll need to know your scope’s objective diameter, usually the last and largest number in a scope’s specifications. This will be used to determine the clearance needed for your scope. The next important measurement you’ll need is the scope tube, and thus what ring diameter is required by your scope, usually 1″ or 30mm.

You need to know what mounting system your rifle is equipped with; receiver grooves, Picatinny rail, Weaver dovetail base, or nothing at all. The type of firearm you have and in some cases, what barrel type and contour, will also impact what mounting system you will need to use. A flat-top AR-15 has vastly different ring requirements than a Remington 700 with a tapered barrel.

The Basics
The most common setup used, and inquired about, for putting optics on a long gun is mounting a traditional magnified rifle scope to a traditional bolt action rifle. Let’s use this setup to explore the basics of putting a scope on a rifle. Traditionally the scope is held onto the rifle by “rings” which are clamped around the body of the scope. In turn the rings are attached to some sort of “base”, which are normally then attached to the rifles receiver or action.

To add to the confusion, there are many variations of all of these components. There are ways mount a scope that combine some or even all of these individual components. (An example would be mounting an EOtech HWS to an AR-15 rifle, where the scope has an integral mount that does not require rings, and the rifle has an integral rail that does not require a base.)

The base is the part of the system that allows the attachment of the scope rings to the rifle itself. Traditionally bases are attached to the receiver of a firearm by some sort of screw or bolt. Some rifles have built-in bases that are integral to the firearm.

Bases are usually specific to the make and model of firearm for which they are designed, and most are specific to the type of rings that can be used with them.

The Ring you select must be the same inner diameter of your scope’s tube diameter, which makes sense. The rings clamp onto the main tube of the scope, so they must be the same size. Most scopes are 1 inch in diameter and so are most rings, but there are many 30mm scopes and rings, and a smattering of other choices, such as 34mm. The other end of the ring attaches to the rifle’s base, so it too must be compatible with that particular base.

The important thing to remember is to match the rings with the scope and the base.

Ring Height
Scope rings come in varying heights to vary the distance from the scope’s centerline to the firearm’s base or receiver. The different ring heights allow you to mount scopes with different objective sizes and also to mount the scope in the proper place for a quick and proper cheekweld. Rings normally come in low, medium and high heights. There are extra low and extra high variations from some manufactures. Ring height is one of the most confusing options for new gun owners.

The traditional mantra is that scopes should be mounted as low as possible without the front of the scope, the objective bell housing, touching the barrel. Also bearing in mind the need to the back of the scope, the ocular bell or eyepiece, to clear the bolt handle. The thing most often ignored in this choosing scope ring height is the need for the scope’s height to match the shooter. When the rifle is shouldered quickly, the scope should be at the correct height to look through it, without any additional movement on the stock up or down to get a good view through the scope.

Remember though that there is no “perfect” ring height that would suit every person, as each person’s physiology is a little bit different. There is a standard ring height worth noting, as it gives an excellent starting point for 90% of gun owners.

In this illustration from UTG, Ring height is measured with “C”

Ring Height According to Leupold

  • 50mm objectives will almost always use HIGH rings in a given style. In certain instances, such as with extremely heavy barrels or some makes of firearm, EXTRA HIGH rings may be necessary.
  • 42-45mm objectives will almost always use MEDIUM rings in a given style. In certain instances, 45mm scopes may require HIGH rings.
  • 40mm objectives will almost always have enough clearance with LOW rings in a given style, though MEDIUM rings will give slightly more clearance, particularly when using a barrel with a thicker shank portion or a heavier contour.
  • 28-36mm objectives will almost always use LOW rings in a given style. Again, in certain instances of a heavy barrel or heavy shank portion of a custom barrel, MEDUIM rings may have to be used, but LOW rings will almost always suffice.
  • 20-24mm objectives will almost always be able to use LOW rings, but in some cases may also use EXTRA LOW rings. In this instance, bolt handle clearance of the eyepiecel will come into play more so than objective / barrel clearance and should be carefully considered.

No Leupold riflescope will fit into EXTRA LOW rings if using a one-piece base.

Ring Height According to Weaver

  • Use low 1″ Rings for up to a 38mm Scope Objective
  • Use medium 1″ Rings for up to a 40mm Scope Objective
  • Use high 1″ Rings for up to a 44mm Scope Objective
  • Use extra high 1″ Rings for up to a 50mm Scope Objective
  • Use 30mm Low Rings for up to a 33mm Scope Objective
  • Use 30mm high Rings for up to a 44mm Scope Objective

For a more in depth look at ring height click here to refer to our ring height article.

Now that we have discussed ring height standards, there are some notable exceptions: for the AR-15 and M-4 series of rifles with “flat top” receivers extra-high rings are the rule of thumb, but some applications use high rings. Also, for mounting a scope on a Harrington and Richardson Handi-Rifle or the NEF Pardner you will need at least medium and perhaps high rings clearance between the scope’s eyepiece and the rifle’s hammer.

Mounting Systems
The most common scope mounting system is the Weaver system. The weaver system utilizes flat dovetail rails with crosswise slots found on everything from rifles to shotguns to handguns. The Weaver style bases are 7/8 inch wide and are designed to accept Weaver style rings. Most rings manufacturers make a Weaver style ring and/or rail. On Weaver style rings the bolt used to secure the ring runs underneath the web of the ring and fits into a corresponding crosswise slot in the Weaver base. This prevents any scope movement fore and aft under recoil or abuse. The bases can be found in one or two piece configurations and can be made of steel or aluminum. The Weaver style system allow the Weaver ring to be detached from the base with the scope still in the rings and reattached without any major loss of zero. The optic can be removed from the gun for maintenance, transportation or storage. The weaver system also allows for using different optics on one weapon or one optic on different weapons.

Picatinny and MIL-STD-1913
Picatinny rails are very similar to Weaver rails. The difference is a published military standard. The physical difference between Weaver rails and Picatinny rails are the width of the slots that are cut crosswise in the base, and the spacing of these slots. The slots in Picatinny bases are wider than slots in a Weaver base, and the spacing of these slots in a Picatinny rail is consistent and standardized. The Weaver style rail’s spacing of the cross slots are not standardized and the spacing is left up to the manufacturer. The recoil lugs on Picatinny rings are thicker to fit in the corresponding wider slots in the Picatinny bases. Weaver rings will fit on Picatinny bases, but Picatinny rings won’t fit on Weaver bases.

22 Rimfire Rings, Tip-Off Rings and 3/8″ Dovetail Rings
Most .22 rimfire rifles and airguns produced today have cuts running lengthwise in the top of the receiver to mount rings on. Some European .22s and air rifles have grooves that measure 11mm or 13mm. 3/8″ dovetail rings are clamped into the groove of these grooved receivers, these rings are also referred to as rimfire rings, .22 rings, and Weaver brands them Tip-Off rings. There are also rifle found with 3/8″ bases attached to the receiver with screws as a normal base would be, and you can buy 3/8″ bases to add to most firearms without them. Some rifles with a grooved receiver are drilled and tapped for Weaver style bases. We recommend using a Weaver style base in these cases as they offer more area for the rings to grab and are more secure and stable.

Redfield Style
The second most common mount type is the Redfield style. This type of mounting system, like the Weaver, has many clones and manufactures of bases and rings. The bases can be one or two pieces, and are known for their sleekness, and strength. Unlike Weaver style rings, Redfield style rings are not detachable from the rails system. The top half of the rings must be separated from the bottom half to remove your scope. The front ring in the Redfield system has a dovetail that turns into a corresponding slot in the front base, allowing the scope to pivot around this point. The rear ring in the Redfield system sits on the base and is held by two opposing windage screws tightened into the ring. The windage screws have a leading edge that fit a corresponding slot in the ring. By loosening out one screw and tightening the other, the ring moves right and left on the base, acting as an external adjustment. This adjustment allows you to zero the windage of your scope without using its internal adjustments.

Dual Dovetail (DD) Systems
Dual dovetail bases are the same as Redfield style, but instead of the windage screws holding the rear ring to the base, the rear ring is turned in just like the front. This system does not offer the windage adjustments that the standard Redfield style bases offer. This system is secure and a very strong system for heavy recoiling rifles and handguns.

Clamp-on Mounts
Clamp on mount such as made by B-Square, S&K, ATI and other manufacturers allow easy scope mounting on guns that aren’t drilled and tapped for scope mounts. These mounts typically do not require gunsmithing, and are easily removed without any modifications to the firearm. Older and military surplus firearms often benefit greatly with these style mounts.