I only moved this post here from another.
CDR Xfire wrote this excellent tutorial.

The link is to an article that I wrote several years ago, for a reader that was having difficulty with an 03A3. It may not be helpful if you're shooting an 03.

Like the 03A3, front sight blades for the 03 came in various heights. I don't have any specific drawing information handy on the range of heights. In the picture the blade on the left is an 03A3 "A" blade, on the right is an '03 blade, and if you look close, you can make out the ".400" height marking.



At the armory, during targeting, an attempt would be made to select the height of the front sight so the point of impact would match the markings on the rear sight as close as possible, with service ball ammunition. At the short sight radius of the '03, a difference in height of .005" will move your point of impact one minute-of-angle (MOA), or 1" at 100 yards, 2" at 200 yards, &tc.

The rear sight of the '03 is continuously adjustable for both windage and elevation, so you should be able to get a good zero with just about any ammunition. The slides on my '03's can be lowered slightly below the 100 yard mark.

Making precise changes in elevation is difficult without one of these, though:



This is Ray Brandes' replica of an O'Hare micrometer, which was an indispensible accessory for shooting the '03 on the target range in it's heyday. You can purchase one here:

www.ray-vin.com/frsights.htm

If you are at all serious about hitting what you aim at, I can highly recommend this widget.

If you have difficulty seeing through the aperture, it can be opened up quite a bit and still meet the "as-issued" dimensions. Service rifle (not "match rifle") rear sight slides were made with apertures from .040" through .090". Slides were marked on the front face (away from the shooter) with a single numeral to identify the size: Numeral 4 was .040", numeral 5 was .050", &tc. The "standard" size was initially the No. 5, but this was later changed to the No. 6. When the rifles were packed for shipment, all of the rifles in the case would have the "standard" aperture slide installed, but an assortment of "alternate size" aperture slides was packed in the crate (see Brophy). When rifles were returned for depot overhaul, those with No. 5 apertures had the apertures reamed out to No.6; the numeral 5 was "X'd" out, and a numeral 6 was stamped on the aperture slide. Most of the WW II production aperture slides were unmarked, but they seem to be a nominal No. 6 (RTL may be able to verify).

I have a few No.7 and No. 8 marked slides, and I can see the front sight and target much better with the larger apertures. I would not alter a marked aperture slide, but I have bought a few spares of the unmarked WW II aperture slides, and carefully reamed out the aperture with a rat-tail jeweler's file from the front of the aperture by turning the file counter-clockwise, so it won't tend to advance and jam. (BTW, Paddy O'Hare and others made a special reamer for doing this, and it was sold on Commercial Row at Perry in the 20's and 30's. It was just one more accessory that no serious '03 shooter could live without.) The No. 8 size works best for me, so when the opening is about .080", I put a little cold blue on a round toothpick to blacken the aperture. If you don't do this, light reflections in the aperture itself will cause you fits.

FWIW, Army Ordnance never had a "No. 10" aperture slide; No. 9 was as high as they went. The special configuration USMC rear sight aperture slide had a .100" aperture, and could be called a "No. 10", but it wasn't Ordnance "issue".

If you like to use the battle sight ... that skinny little notch with the ladder down ... you will shoot way high, as the "battle zero" with M1906 ammo was about 547 yards. In the National Matches, and in the military qualifcation course with the '03, all firing at 200 and 300 yards had to be done with the battle sight. Old timers told me of holding on the very bottom of the target frame at 200 yards to get "5". You can improve the situation today by substituting an 03A3 front sight blade for the shorter '03 blade. You'll have to file a bit off the bottom of the 03A3 blade to get it to fit in the '03 moveable base (the red lines in the first pic show this). The range markings on the rear sight ladder will be way off for service ball ammunition, but the "battlesight zero" will be about 100-150 yards, depending on what ammuntion you are using. And if you get one of the Ray-Vin micrometers, you can just ignore the range markings on the sight, anyway ... you just count clicks on the mike when you use the ladder "up".

Are you confused yet??

Resp'y,
Bob S.