Important info for Cast Bullet shooters

[NuJudge]

A series of posts by "Bob S" on another board gave the incremental changes in Minutes of Angle for the rear sights on the M1903A3 and M1917 rifles. This information is particularly valuable to cast bullet shooters. I thought I would plagarize it here, with attribution:

For the M1903A3:

"One click on the windage screw is 1/4 turn of a 32 tpi thread. 1/128" = .0078". That's about 1 MOA at the sight radius of the 03A3.

Elevation table:

Change in Range MOA
200-250 1.5
250-300 1.7
300-350 1.9
350-400 2.1
400-450 2.1
450-500 2.1
500-550 2.4
550-600 2.6
600-650 2.8
650-700 3.0
700-750 3.3
750-800 3.8

Recognize that this sight is not a Redfield International. There is a significant amount of variance between individual sights, expecially in the elevation adjustments. Some of the detents on the ramp look like they were cut with a dull hacksaw, some look like they were lightly scribed with a scratch awl. Still, with some tightening, reasonably precise adjustements can be made. Pretty amazing considering the crude design and construction of the sight."


For the M1917:

"The sight radius with the ladder up is 31-5/8", so the value of sight change that equates to one MOA is .0092". (sight radius x TAN (1/60))


200 to 300: 2.6 MOA
300 to 400: 4.1 MOA
400 to 500: 3.9 MOA
500 to 600: 4.6 MOA
600 to 700: 5.8 MOA
700 to 800: 6.3 MOA
800 to 900: 7.6 MOA
900 to 1000: 8.4 MOA
1000 to 1100: 9.3 MOA
1100 to 1200: 11.1 MOA
1200 to 1300: 11.7 MOA
1300 to 1400: 12.7 MOA
1400 to 1500: 14.1 MOA
1500 to 1600: 15.3 MOA

The changes in the mid-and longer ranges will probably be of interest only to those who shoot mild cast bullet loads. We usually have to work in the 700 to 1000 yard settings on as-issued military sights when we are shooting at 100 or 200 yards.

My front sight adjuster is British, and the screws are 22 TPI. One full turn moves the sight 1/22 inch, or .0455". Using the .0092" per MOA, one full turn of the screw is worth 4.94 MOA, so figure 5 MOA per full turn, 2-1/2 MOA per half turn; 1-1/4 MOA per quarter turn. It can be used with one hand, so you can stay in position and in the sling to get centered up during the sighting period. After that, just take favors if need be."

I hope you all find this as interesting as I do.

CDD