Ok, does anyone have the reference table for the mount spacing for Unertl Target telescopes.

I have blocks on my Stevens-Pope.  The blocks are for the Winchester and Unertl/Lyman scopes (Steve Earle product).  I have the six page Unertl instruction manual for adjusting the scope for range / parallax, etc.  But, I think Unertl also published a chart that told you depending on the spacing of the mounting blocks how it effected the point of impact, etc.  The scope I have is a 1.5" 20X Target Scope.  

stebbinsgr,
Here are the mount spacing for Unertl bases.
5.4"    = 1/3"  Per Click.
7.2"    = 1/4"  Per Click.
9.0"    = 1/5"  Per Click.
10.8"  = 1/6"  Per Click.
12.6"  = 1/7"  Per Click.
14.4"  = 1/8"  Per Click.

The Info came direct from John Unertl years ago and they are now on the Unertl Group at: 

(You need to Login or Register to view media files and links);

There's a lot of Info on Unertl Scopes on that site, probably more than most need to know,  there's info on how to ID the diferrent models, take them apart for cleaning, and changing crosshairs. 

Also has the instructions on how to set up any model of Unertl Scope, including your 1.5"  20 X.
 S T 

Boats,

You raise a very good point.

The 7.2" spacing is standard for the Lyman Junior Targetspot and Super-Targetspot scopes as well.

One other consideration, when you space the bases out further, you use up the allowable range of adjustment faster.

BP

Here is the formula, from memory, so double check me anybody

Example

Distance to target in inches, 100 yard=3600 inches divided by sight radius, say we are using a tang sighted single shot. 36 inch sight radius = movement required to move point of impact one inch.   3600 divided by 36 equals 1/100 of one inch movement required for 1 moa

Take a external adjustment scope with 7.25 inch spacing it's the same formula  3600 divided by 7.25  takes 1/496 of an inch movement to change point of impact 1 moa.  it's about 1/2000 of an inch in round terms to make 1/4 moa movement on target.   

You can work the formula to solve sight radius, range of adjustment available, scope block or sight height problems etc.

Boats

Trouble with 9 is you get unorthodox clicks.  That's workable but irritating. One of my CPA's with a Mike Stevens Tang is 1.3 MOA per graduation. I can split in half for about 2/3 of a minute.  Sometimes I forget.

Of course shooting all kinds of competition almost all rifles are different, direction of turn can be a major problem.  If every shot counts and sighter target is not available best write it down.

Main thing is know your outfit

Boats

SCOPE BLOCK SPACING
     This is based on my Lyman STS and Unertl scopes.
     Adjustable scope mounts are threaded the same as a micrometer caliper, 40 threads per inch. Thus, one turn or revolution of the adjustment knob = .025”, twenty-five thousandths of an inch. The mounts have 25 graduations per revolution, so one graduation = .001”, one thousandth of an inch. There are two clicks per graduation, so a click = .0005”, half a thousandth of an inch.
     Scope blocks are most frequently spaced such that the block flycuts or mounting points are 7.2” apart. This results in a movement of the scope reticle of one quarter of an inch at 100 yards, sometimes called a quarter of a minute of angle. Then the scope adjustments are called “quarter minute clicks”. (1” is close to 1 MOA at 100 yards.)
     Sometimes other center distances of the block flycuts or mounting points are desired or encountered. 
     Let “CD” = block center distance, and call the reticle movement per click “MOA”.
     Then 1.8/CD = MOA,  1.8/7.2 = .25, for example, and
     1.8/MOA = CD, 1.8/.25 = 7.2 for example.

     While the graduations go further, adjustment range of scope mounts is ~ .2” which works out to about 100” at 100 yards with 7.2” scope block spacing. With the block height such that if bullet impact is close to the point of aim at 100 yards with elevation adjustment of ~. 01” or one line; then any range up to 1000 yards is normally within the adjustment range of the scope. 
joe b.

That is great. Thank you. I'll scan and post the Lyman Super Targetspot manual in the similar Lyman scope thread, once it arrives.

NoBears it's geometry who made the scope makes no difference.  Scope or any rifle sight is just a angle measuring device.  Think of your rifle barrel and iron sighting system as a Stadimeter ,Scope is more like a Sextant shorter radius and has optics.  All it does is measure angles precisely.

Boats