The battle sight zero on an M1 Garand happens around 300 yards, so sight in at 25 meters (82 feet) and then go up three more clicks. At 25 meters, this means you will be about 3/4 inch above your point of impact. The reason for this is that at a 25m zero, the bullet will cross the line of sight at 25m and at 200 yards, so the 25m zero is also dead on at 200 yards. The sights on the M1 and the M1A/M14 are adjusted in 1 MOA clicks. To go from 200 yards to 300 yards, adjust up 3 clicks.
The sight adjustment pattern looks like this:
100 to 200 yards, increase 3 clicks
200 to 300 yards, increase 3 clicks
300 to 400 yards, increase 3 clicks
400 to 500 yards, increase 4 clicks
Just remember 3,3,3,4 and you will be in the money for shooting 20 inch targets out to 500 with the irons. The front sight on most M1 Garands and M1A/M14 rifles is set at 7 MOA, although this will vary a little bit depending on your specific distance from your own eye to the front sight. Basically you need to go to the range and measure the size of your own front sight against a piece of paper with different sizes of targets. Make a sheet of paper with different size squares on it from about four inches to ten inches. Then compare your front sight to those squares downrange.
The roughly 7 MOA front sight was chosen so that you could know whether a 20 inch target is inside or outside your battle sight zero. If a 20 inch target is larger than the front sight, then it is closer than 300 yards. If the target is smaller than the front sight, the target is farther than 300 yards.
National Match sights are supposed to come in around 5 MOA for the 0.062 width, but you must calibrate the sight to actually get it right. This does not affect trajectory of course, just the precision of your ability to range targets using the front sight, and if you ask me, the NM sights are far better, although a lot of people with aging eyes don't like them as much as the wider front blade.
To use the rear sight drum, I ignore the numbers and just memorize the number of clicks each range is from where the sight bottoms out. So, I suggest sighting in at 100 and then counting how many clicks you need to go down to bottom the sight back out. If you are wanting to use the elevation drum with the numbers on it, here is how you do it.
1) Sight in at 25 meters (82 feet);
2) Then slowly count the number of clicks it takes you to bottom out the sight;
3) Remember the number of clicks, or write it down on a piece of paper;
4) Elevate the rear sight the same number of clicks;
5) Now loosen the screw on the left side of the elevation drum until the elevation drum spins freely;
6) Set the sight at 200;
7) Tighten the screw;
8) Verify that it is the same number of clicks to bottom the sight as it was when you first counted.
This should take care of you just fine as long as you are using the M2 Ball ammo that J Garand designed the calibration of the rear drum for.
I hope this helps,
M1Amen
PS, just as a side note, don't trust the elevation pinion. The other posters are correct that they can come loose. You want to use the 3,3,3,4 that I mentioned earlier.
