I finally found an example of this sight, now that I got it in my hands I regret buying it, it's a real POS! I believe they were intended for bolt action shotguns or other guns with a wide rounded top, like pump rifles and shotguns. The bottom is curved and fit the contour of a Savage 170 (same receiver as the pump shotguns). The one on the 99 is on an adapter that was probably not of factory issue and the sight was probably never intend for use on a 99. Still don't know who made it, I also doubt they ever actually patented it. This sight also is rather larger and would easily to bend out of shape with the thin sheetmetal construction.

These sights are not very good, it's hard to adjust and after adjustment when tightening everything down the sheetmetal base flexes and everything moves a little. The adjustment consist of inner and outer eccentric rings secured by a strap. There are indicator marks on the strap going both way from the top marked at the 5 & 10 positions both sides. To adjust the elevation the outer ring is turned a number of marks in either direction which will raise or lower the aperture by moving it in an arc - so both the elevation and windage settings change - the inner ring then has to be turned the same number of marks the opposite way to put the aperture back on vertical center. The outer ring is split so when the strap is tightened if clamps onto the inner ring. None of this works very well. Although windage could be adjusted with this sight having the aperture other then centered would mean any change of the rings would affect both elevation and windage and it would be total guess work on which ring to move and how far.

The rings have a wider space in the knurling @180° for indicator marks to set the rings - with them set at 0 the elevation is in the middle of it's range. This example has had a corner of the base cut off. [Linked Image]

[Linked Image]

A couple other 'possible' uses where there might be a reason for the cut corner, one to clear a safety and one to clear a bolt handle keeping the sight as far back as possible, the radius on the mounting bracket is to larger for these 22's and the sight would rock if not shimmed.

[Linked Image]

[Linked Image]

The large opening around the small sighting aperture does help get on target fast by giving a wider view. This is not a new idea, here is a 'Killdeer' sight from the early 1900's that offered something similar.

These are old photobucket pictures so I'm not sure how well they will display, is at all.
[Linked Image]
[Linked Image]
[Linked Image]
[Linked Image]

Link to the patent if the pictures don't show - uspto.gov=00810761






Gene