Unertl, Lyman and Fecker all used the same type of base for mounting. The base was/is typically attached to the barrel instead of the receiver. Bases were made in different heights, short, medium, etc. If I recall correctly there were different heights available. Additionally, the front base was shorter in length than the rear base. I know of only one source of supply today, CPA in Pa.
http://singleshotrifles.com/sights.htmlBasics on mounting the scope. You need to be careful here. 7.2" ctc between the front and rear base is critical.
This was copied from a post on the assra.com site.
TELESCOPIC SIGHTS
Telescopic sights may be categorized as "Outside Adjustable" and "Internally Adjustable."
Outside adjustable telescopic sights include Lyman Targetspot and Super Targetspot, Unertl, Litschert, Fecker and Davis brands. These have adjustments built into the mounts that are (mostly) click adjustable and clearly readable so that settings may be recorded. They have adjustments on the rear for focusing the crosshairs, and on the front (Fecker in the center) for eliminating parallax. It is entirely practical to move these sights from rifle to rifle, re-setting the sights each time.
These sights attach to "scope blocks" on the rifle barrel, which are most often 7.2 inches on center.
The adjusting knobs are marked in 25 divisions, and there is a click between each division, so there are 50 clicks per revolution of the knob. Each click moves the telescope one-half of one thousandth of an inch, .0005". Divide 3600 inches in 100 yards by 7.2 inches center distance between scope blocks and you get 500. Then multiply 500 by .0005" per click and you get .250" or a quarter inch or about a quarter minute of angle shift in bullet impact per click.
