Sub-Base for Top-Mounted Gunsight

1. Field of the Invention

The present invention relates to the mounting of telescopic sights on guns, especially on semiautomatic shotguns. It is necessary for the telescopic sight to be rigidly mounted to the gun so that the line of sight is precisely parallel to the bore of the gun. Moreover, the sight's rigid mounting must withstand repeated heavy shocks from the recoil of the gun as it is fired. That is, the sight must be mounted so rigidly to the gun that the repeated heavy shocks do not generally affect the precise parallelism of the sight's robe and the gun's bore. Though occasional adjustment may be necessary, this parallelism must be maintained insofar as possible.

2. Prior Art

Most guns, especially semiautomatic shotguns, have a receiver made from metal that is substantially thinner at the top than at the sides. The top of the receiver is thus too thin to permit tapping and drilling for screws strong enough to hold the mounting for a conventional telescopic sight. On certain guns, e.g., Browning Model A-5, Remington Model 1100, and Remington Model 11-87, the receiver is so thin at the top that only two to two-and-a-half threads may be drilled therein. So few threads are insufficient to hold the mount for a telescopic sight to the gun with sufficient rigidity to withstand normal use. A sight mounted with screws held by only two to two-and-a-half threads will quickly work loose in response to the gun's recoil when it is fired. A loose sight or one that is not rigidly mounted will cause shots from that gun to be inaccurate. Indeed, when a telescopic sight is attached to the thin top of a conventional receiver on a semiautomatic shotgun, the recoil from a single shot can detach the sight, thereby endangering the shooter. Such an accident is likeliest when the gun' s receiver is made of aluminum, which is a relatively soft metal.

Hence it is conventional for gunsmiths to mount a telescopic sight on such a gun by means of a side mount, such as a Weaver mount. Such a side mount is used because the side of the receiver on such a gun is sufficiently thick to hold the mount rigidly, having a thickness that supports approximately five threads. Unfortunately, however, mounting the sight on one side of the gun creates unnecessary bulk, in that a side mount projects from the gun at an angle of approximately 45 degrees from the vertical to clear the gun's receiver and then reverses to place the sight into vertical alignment with the gun's bore. A side-mounted sight is also difficult to align with the bore. Thus mounting a sight from one side only in the customary way can reduce both the comfort of the weapon and the accuracy of fire. Moreover, because a side mount is installed on one side of the receiver only, the sight it holds may work loose from the gun.

The principal object of the present invention is to permit the mounting of a telescopic sight on a gun in the most advantageous position, namely, on the top surface of the receiver.

Another object of the present invention is to provide a gun with a top-mounted telescopic sight that can withstand the repeated shocks of recoil without shifting out of alignment.

Still another object of the present invention is to mount a telescopic sight on a gun so that the sight and the gun will in general never move relative to each other, thereby keeping the sight always substantially in calibration relative to the gun's bore.

A further object of the present invention is to mount a telescopic sight on a gun so that it can be removed and reinstalled without changing the sight's calibration.

The present invention is hereinafter described in more detail with reference to the accompanying drawings.

FIG. 1 shows in perspective the sub-base of my invention mounted upon a gun such as a semi-automatic shotgun.

FIG. 2 shows the sub-base of my invention in plan view.

FIG. 3 shows the sub-base of my invention in side view.

FIG. 4 shows the sub-base of my invention in bottom view.

FIG. 5 shows the sub-base of my invention in cross-section.

Referring to FIGS. 1-4, sub-base 10 of my invention is constructed of Aluminum or other rigid metal of a thickness of approximately 0.125". It may be constructed by (1) cutting aluminum tubing of the proper diameter (approximately 1 5/8" outside) lengthwise into three substantially equal pieces, each of said pieces being further shaped into a sub-base, (2) casting from molten metal by injection, (3) boring and milling from solid metal stock, or by any other method of working metal.

Sub-base 10 of my invention is approximately 5 1/6 inches long and 1 3/8 inches wide. As shown in FIG. 5, sub-base 10's cross-section is substantially in the shape of a 120-degree arc of a circle. Sub-base 10 is machined at bottom surface 12 to fit receiver 13 of the particular gun to which it is affixed. For mounting to those guns that require it, sub-base 10 may have port 15 cut out on the right or left side. Top surface 14 of sub-base 10 is drilled, and holes 16 are tapped to accept base 17 of a top, pivot, or see-through mount for a telescopic gunsight held in place by screws 18. A line 21 shows the vertical axis of the gun and sub-base 10.

Sub-base 10 of my invention is rigidly mounted to receiver 13 by means of a plurality of screws, approximately four to six (19). Screws 19 fit through holes 20 in sub-base 10 that are drilled through its sides at an angle substantially 45 degrees from the vertical. Screws 19 engage holes at a similar angle drilled into both sides of receiver 13 and tapped to a depth of approximately five (5) threads. Because sub-base 10 of my invention is rigidly held to both sides of receiver 13, sub-base 10 resists working loose under the repeated impact of recoil. Telescopic sight 22 mounted to sub-base 10 of my invention will therefore have its axis held precisely parallel to the gun's bore and remain in calibration for as long a time as possible.

The foregoing description of the preferred embodiments of the invention is presented for the purposes of illustration. It is not intended to exhaust the invention or to limit it to the precise forms disclosed, since many modifications are possible in the light of the above teaching. The scope of my invention should be limited not by this detailed description, but rather by the claims appended hereto.