Enhancing Action Rigidity With A Scope Base

It has been proven that even a short section of horizontallysuspended railroad track will have a finite flex or bend to it. As I pondered these phenomena I wondered just how much measurable flex or springing there may be in the action of a rifle produced by a horizontally-suspended, heavy rifle barrel. This prompted me to accomplish a series of pretty convincing tests. This was done with a magnetically mounted dial indicator spanning the length of a rifle receiver as a means of testing for flex or springing.

The tests were performed both with and without a one-piece scope base and a method of controlled flexing of the rifle receiver. I began by strengthening the attachment of the one-piece Picatinny base by replacing the existing 6-48 base screws with 8-40 screws and adding two extra screws in the process. The base couldn’t be attached more solidly short of bonding it in place.

Subsequent tests for action flexing or bending were monitored The added central action screw was both used and removed during further action flex testing procedures. both with and without the scope base screws tightened down. The fundamental dynamics of the test involved placing a barreled action horizontally in a good, sturdy bench vise with a means of variable controlled flex testing.

With the rifle barrel solidly immobilized in a vise, a dial indicator was placed in position, suspended on an arm spanning rearward the entire length of the horizontal rifle receiver, thus enabling a reading to accurately indicate the smallest amount of downward flexing movement in the rifle receiver. The principles used in testing action flex or movement in this way are pretty straight forward.

A 16-inch length of steel rod, the exact size of a rifle bolt, is placed about two inches into the receiver bolt hole retained by horizontal friction. Any changes in action flex are shown on the dial indicator. A 10 – pound barbell weight is then carefully slid in increments over the rod from the receiver outward. As any changes in action flex take place they are seen on the dial indicator. I performed initial tests with the scope base screws loosened at one end.

Then, the weight was moved outward in consistent increments, with the measurement on the dial noted and recorded. I used a marker on the rod as a means of uniformly positioning the barbell weight. The sequence of testing is less important as long as things are controlled uniformly. In my initial testing I removed both the barbell weight and the steel rod and tightened all six of the scope base screws securely. The steel rod was replaced and the aforementioned stress tests repeated. The

Six larger 8-40 base screws replaced the four 6-48 screws as normally used on this receiver. The Near Manufacturing (NearMfg.com, scope base had the six pre-drilled screw holes for 8-40 screw application. Receiver required the addition of two holes and enlarging the existing holes to 8-40 size, a very worthwhile procedure. results proved to be consistent.

The amount of measurable action flex or springing is essentially linear movement and will vary with the type of rifle action tested, or type and method of scope base used, and/or action screw quality or arrangement. For example, a solid, cylindrical action like the single-shot Remington 40X or Savage Models 12 and 112 compared with those rifles with magazine cutouts like the Winchester Model 70 or Ruger Model 77 will shot a marked difference.

In conducting these tests, barrel shoulder to receiver axial preload must be at normal full torque and the barrel must not extend be- Dial indicator reads zero with rod in bolt hole. This included loosening and tightening of the base screws and repositioning the barbell weight. Few actions would be totally immune to some measurable flexing in these tests.

Addition of a one-piece scope base proved conclusively that reduction in receiver flexing takes place, which is further reduced with a properly-applied central action screw and pillar. yond the vise jaws. We are merely demonstrating here that a flex or bend does indeed occur more readily in some actions, particularly those with magazine cut out. The method I have used here readily proves this.

Central Action Screw Support Some might argue against the merits of adding a central action screw as a means of improving overall action rigidity and resultant accuracy. While I may not be the forerunner

M. O. target scope to the solid aforementioned one-piece scope base on the Winchester Model 70 Stealth II rifle receiver. Early accuracy tests that followed were eye opening. The measures that added rigidity to the overall action showed a very worthwhile improvement. of this modality it has enabled me to enhance and improve accuracy in a wide variety of rifle actions, including rigid receivers like the Remington Model 40X and Savage Models 12 and 112.

I have made the addition of a third action screw and well-placed pillar in a number of magazine-style rifles as well and all have shown at least some improvement in rigidity and resultant accuracy—some surprisingly so. In any case, accuracy has never worsened. This had encouraged me to convert a good many repeater style actions to single-shot status, replete with loading ramps. In most instances accuracy has been noticeably improved. This will be covered in more detail in a subsequent article.

Conclusions Not surprisingly, the less obvious things we do can sometimes make a significant improvement in rifle accuracy. Though this may be particularly noticeable in the more accurate rifles where the difference in groups are more prominent, it stands to help the varmint hunter or even the longrange, big-game hunter as well. AG 30 caliber Magnum cartridge. A Krieger 1 in 10 twist barrel was used, along with the following loads.

Two groups on the left measure 0.390" and 0.289" fired with 168 grain Berger bullets and 45 grains of XMR 4064 powder. Two groups on right were fired with a 168 grain Sierra pushed by the same propellent charge. Upper (10 shot) group measures 0.375" and the lower right is 0.450". American Gunsmith Reader Services 1.