External adjustment rifle scopes

[glindes]

Gents, et al:
Request, please. Are there any publications available that explain (Unertl) operation of external adjustment rifle scopes?
Thanks in advance, Geoff

[raymeketa]

Geoff

Exactly what instructions are you looking for? An external adjustable scope needs an adjustable mount since the internals of the scope are fixed.

Maybe I am not understanding your question.

Ray

[mhb]

If you are asking about the method of adjustment...

the elevation and windage screws are true micrometers: that is, they are designed to move .001" (in the older models), and .0005" per click in later types.
The bases to which the actual mounts are attached are spaced 7.2" apart (center-to-center) in standard installation, which, for each click of either screw, gives 1/2 (or 1/4) MOA adjustment per click - which is achieved by actually pointing the whole telescope in the appropriate direction (opposite that in which the POI is desired to move).
The knobs and the bodies in which the screws move are calibrated exactly like a micrometer, and the readings can be read and recorded in exactly the same way, though, for convenience, most shooters refer to the readings as so many MOA.
mhb - Mike

[glindes]

external adjustment

I'm a recovering engineer. I may just be over-thinking it. I'd like to get an Unertal manual or catalog. TIA Geoff

[Cosine26]

Here is a copy of the Unertl Instructions. Hope this helps.

http://i116.photobucket.com/albums/o15/Cosine1/Unertl/unertl1a.jpg

http://i116.photobucket.com/albums/o15/Cosine1/Unertl/Unertl2a.jpg

http://i116.photobucket.com/albums/o15/Cosine1/Unertl/unertl3a.jpg

Telescope mounting block spacing
Recently there has been some discussion about mounting and using Unertl, Lyman and Fecker target telescopes of the 30’s, 40’s and 50’s so I thought that I would add my input.
In the 30’s through the 60’s there were two standard mounting distances for the blocks of these telescopes and one non standard. The first was standard mounting distance of 6.86 inches and the second was 7 3/16 inches. The non standard distance was 6.0 inches.
On these scopes the thread of the mounts was 40 tpi so that each revolution of the knob moved the mount 1/40 or 0.025 inch. Using the 6.86 inch distance caused the scopes to move at MOA while the 7 3/16 spacing caused the scope to move in “inches per hundred yards”. The early scope mounts had “clicks” at ½ MOA or ½ inch intervals while the later mounts had clicks at the ¼ increment. For most people in the 30’s who were interested in using the NM ammo, the ½ MOA (6.86) spacing was important so that the standard Army Tables of fire could be used. After WWII the 7 3/16 spacing became popular since NM ammo was not available so that the Army Tables of Fire were not important. The scopes were increasing used on small bore (.22 RF) where the targets were well known in the “inches” measurement. The 6.0 inch measurement was used by those who wanted to mount both blocks on the barrel of the M1903. This dimension gave satisfactory eye relief but the adjustment now was 0.30 inch per hundred yards as opposed to the 0.25 inch per hundred yards. The Model 70 Winchester Bull Gun came with a standard block on the receiver ring, but the front (barrel) mount was elongated and contained notches where the shooter could select either the 6.86 or the 7 3/16 spacing.
All that having been said, most of us rarely used such fine adjustments. Mechanical scope mounts of the day were subject to mechanical error in adjustment. A ¼ click adjustment may or may not move the POA by ¼ inch or MOA. Most of us used the Ted Sloan score books and the 1000 yard target was marked off to show MOA on the target. (So were the other target score sheets). We would just hold off a quarter or a half to make small corrections. I have held as much as 2 minutes. Moving the cross hairs on the target moved the LOS and consequently the LOB while the mechanical adjustments may or may not do so.

In addition, and I probably will be taken to task for this as I already have, we disconnected the recoil spring, not because it was ineffective, but because it was too effective. The popular 1000 yard Bull Guns of the day were usually some flavor of 300 Magnum (H&H, Norma, Winchester, and some wild cats) shooting 180 or 190 grain match bullets ahead of 60+ grains of 4350 or 70+ grains of H4831. (I won’t give the exact loads for these were either DuPont or Hogedon powders of a long gone era and do not equal today’s powders.) Even in a 14 pound Bull Gun the recoil shooting with the cloth 10X jackets was brutal. The Rifle would recoil, while the inertia of the scope would tend to keep it in is spacial position. This would cause the scope to compress the spring which would then drive the scope back into the shooters eye. Not good! After each shot we would reach up and pull the scope back into “battery” using a twisting motion for uniformity. Firing twenty shots first with a scope and then with iron sights was a day’s work. In those days at 1000 yards you were allowed only two sighting shots (if any) followed by twenty shots for record. If you did not hit the paper within the first five record shots you were asked to leave the line.
Just a few comment from an old timer.

[raymeketa]

Cosine26 - Thanks for the memories.

Several world class Benchrest shooters have converted their Leupold Benchrest scopes to external adjustments by gluing the guts in place and installing custom made adjustable mounts. I have not done that but they report that it is worth the added work and expense. The erector systems in the best made scopes simply are not reliable. I "Tuckerize" all of my scopes but even they are not infallible.

Now that the difference between a winning group size vs first loser is so small, every little bit helps. Maybe the old ways aren't so old after all.

Ray

[Cosine26]

Redfield once manufactured the "1600" and the "3200" for small bore. As I remember they both used internal adjustments.Have you any experience with either of these?

[glindes]

Unertl

Cosine, Thank you. I'm just trying to get educated...not problem solving. Geoff