Reat Sight Problem

I purchased a nice 1903A3 at a gun show today and took it to the range to see how it shot. The second shot hit the bullseye and I was very happy, but it was all downhill after that. After about 30 rounds, I figured out the issue. The rear sight seems to be loose, at least the part that slides up and down for range adjustments. I can set it at 300 yards and fire one time and it slides to the front. This happens at all settings, it just will slide to the front with the recoil. I attempted to tighten the screw and all I did was bugger up the screw head.

Any ideas on how to address this issue? The screw will not turn to the right or left, someone else must have attempted to tighten it also.

Sounds like you need some new parts. Might be the small plate that screws to the aperture. It must be tight and provide the "click" to hold the ap. If it's worn, it might not engage the slots on the slide.

First things first. You need to get it apart. You must use a 3/16" hollow ground screw driver/bit. Make sure the gun is kept sturdy and still, so you can apply some pressure to the screw. Might wanna soak it in some penetrating oil if you think it might be stuck.

If you need parts, send me a PM. I just took apart two of them.

The little butter fly shaped spring that holds the aperture in place probably does not have a sharp enough notch in it to hold the thing in place, or the notches in the side of the aperture are not deep enough to properly engage the spring. The notches can be deepened with a needle file and the spring can be slightly bent to give it more tension. Be careful when bending.