Picatinny RailBy Norman E. Johnson
©Copyright 2009, Precision Shooting Magazine
My association with the rifle scope and mount goes back a long way. The very first scope mount I had ever used was one I made to mount to a scope, which I also had made from an old brass telescope. This was mounted to a rifle I had brought back to life. That was back in the fading 1940s, but remains clearly etched in my memory. That first mount consisted of two bands of metal encircling the scope, with three triangularly opposing set screws in each band used to hold and adjust the scope. Overall, this scope and mount lacked a great deal of mechanical integrity, but it served a purpose. More importantly, at the age of 14, I was learning.
Shown here is a NEAR Picatinny rail and ring mount on a Winchester Model 70 Stealth II short-action receiver both in and out of the stock. The scope is a Redfield 8X-32X target model. The rail has a 10 MOA slope commonly used by target or varmint shooters from100-500 yards. By comparison, a 25 minute rail angle would permit elevation of 125 inches at 500 yards or 250 inches at 1000 yards. Without the sloped rail base, few scopes would permit vertical reticle setting out to 1000 yards
Since those early times I have made scope mounting a virtual work in progress. Discovering strengths and weaknesses of mounting system adaptability has always remained an important issue to me. Much of this is reflected in my writing over many years. One treatise on the subject that I authored was published in the 57th Annual Edition of GUN DIGEST (2003), entitled, “Stress Elimination in Scope Mounting.”
In my work with telescopic sights, I have used a good share of the scope mounting systems ever designed. For a time, there were few scopes and mounts to choose from, and many of these failed to keep a scope in true alignment with the bore. Rifles required constant resighting to hold zero. The rifle or its load was often blamed for poor performance, when, in fact, the mounting system or scope was the culprit…sometimes both. At the same time, I have had the opportunity of observing great progress in the quality of scopes and the process used in mounting them. Scope and mount manufacturers worked diligently with firearms manufacturers to build a product that would assure a precision fit between the scope base and receiver, maintaining as close a tolerance between parts as is mechanically achievable. I would often be the first to welcome these advances in engineering, and couldn’t wait to try new products. This technology evolution continues to be an interesting part of it all…and there is still progress to be made.
While striving for the final level of precision and accuracy in a rifle, my work would take me deeply into its makeup and function. There were so very many areas where problems could arise. Obviating each and every possible or likely cause of failure requires a great deal of experience and foresight.
I had not ventured far into serious shooting before losing at least some trust in the mounting system of a scope sight. Early on, there weren’t many mounting methods to choose from. Many of us older shooters recall the introduction of some of the forerunners like Bill Weaver’s basic quick detachable, or the Redfield Jr. system, et al. Many rifles were not even drilled and tapped for scope mounting as mounts first came on the scene.
As a mechanical minded individual, I’ve always suspected the overall durability of many scope-mounting systems. Poor basic design was/is the cause for some scope mount inadequacy, and once a company tools up for production, it’s pretty hard to make major changes. Attaching a scope base with the relatively small 6-48 size screw was a sort of design impediment that got started within the shooting industry. Once such decisions are made, it becomes hard to change. So the 6-48 screw became and remains the norm, despite its marginal strength to withstand the required torque to keep some scope bases from moving under heavy recoil or the inevitable displacement of a scope under adverse hunting conditions.
As a long-range, winter predator shooter, keeping a rifle precisely zeroed became extremely important to me. As rifles failed to remain sighted, I put the mounting systems through some extreme tests, along with scores of scopes. Many of the findings of these tests appeared in an award-winning article in the January 1992 RIFLE Magazine, which was entered in a contest sponsored by Leica Optics.
No small number of scope mounting problems can be traced to the scope base, or bases, per se. A scope base has a very vital function. It must fit the gun receiver either as a one-piece or two-piece base. Here both the rifle manufacturers and the scope/base manufacturers must come together on specifications and maintain tolerances that are as close as possible. A few thousandths of an inch in diameter or flaw in alignment, and precision may be compromised. Some manufacturers have gone to integral scope bases like those offered by Ruger, Sako, Tikka and a few others. These built-in bases eliminate the tolerance gap of a screw-on base or bases, which is essentially stacking tolerances. However, the integral bases can still fail to give true coaxial alignment between rings, or provide the additional bridging support over the receiver provided by a good, one-piece scope base. Some conventional, one-piece scope bases are quite frail, but even these tend to add at least some rigidity as a bridging over the receiver cut out.
As a preventative measure for base-to-receiver slippage, some forms of a bonding agent can be used and is recommended by a few. Even pinning the base to the receiver with through holes in the base and into the receiver is done by a few. As I see it, these pins are “forever” measures. Regardless of the benefits of base pinning, I would not consider this method of base stabilization. I swap too many scopes and mounts on my many test rifles to consider this measure of added stabilization; and drilling extra holes in a receiver doesn’t do much for a rifle’s appearance or value. If I did use a bonding agent between base and receiver, it would be something like J.B. Weld or the like. This material has a bonding capacity that would secure a base in place even without screws. Application of heat would release the bond.
The modern-day scope mounting schemes must meet a lot of important criteria. For hunting rifles they need to meet the aesthetic demands of hunters and shooters. They need to be light weight enough to not add appreciable weight to the rifle, and still offer a reliably durable mounting system that allows the rifle to hold a constant zero. Many of today’s scope mounting arrangements meet these needs with little compromise, both in hunting as well as target and bench rest shooting.
The Picatinny Rail Scope Mounting System
We can go a step farther to assure a more durable scope mounting system by using what is called a Rail Mount System, or sometimes called a Tactical Rail Mount System. This system essentially consists of a heavier, one-piece scope base with multiple cross slots to accept heavier-built crosspin style rings. The overall effect of the rail is to stiffen the action and provide a precision surface for these stronger rings to lock into. The remainder of this article will cover the Picatinny Rail Mounting scheme. More specifically, the rail and rings made by Near Manufacturing Ltd., Brownell’s Picatinny scope base and scope rings, and Holland’s Picatinny Rail Mount. There are other Picatinny or tactical arrangements by Warne, Atlas Products, Farrell Industries, Badger Ordnance, et al, all available through Brownells.
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