Yes, you could modify the A2 sight block and keep all the elevation adjustment. That was my original intent but the extra A2 sight block I had was a DMPS and had a different thread pitch and height as compared to the RRA A2 block so it wouldn't have worked. I figured I could modify the original RRA A2 slight block down the road now that the guinea pig test was out of the way.
The modification steps involved counter boring aboput 0.030" by 0.375" diameter into the windage drum sight of the block. This removed most the A2 adjustment dimbles and was needed to get the correct distance from the shoulder of the windage screw to the windage drum roll pin cross hole.
The only major issue was that you do not have room to drill the 0.125" diameter hole for the drum detent spring and plunger. It needs to be on the circular path around the drum but if you drill at the lower portion of the block you break thru to the relieved area where the aperture spring rests. There was no great way to hold the spring and plunger in so I eliminated the detent spring and used the aperture spring to help provide the required spring force for the detent pin. I drilled the detent hole, 0.125" diameter, back into the sight block about the length of the detent pin, 0.235" I believe. This hole broke thru the relief area of the aperture spring area and left a groove about 1/2 the diameter of the hole. I then cut a 45 degree angle of the original spring end of the detent pin and this rides under the corner of the aperture spring. I then cut a slit in the aperture spring to provide a slightly lower spring force to the dentent pin as it hits the 45 degree area of the pin. It's like the multiple fingers on the sear spring of a 1911 pistol. This seems to work good. Nice tight spring force and no way the detent pin can be removed without removing the drum first and the spring force to the aperture is minimally affected. Obviously, time will tell if it works as planned.
Hope this helps explain it a little, in the long-winded fashion.
hanksI modified the above picture to show the modified components. Another thought was that you could change the design a little to allow modification to be completed with simple drill press, or hand drill if your really good.
You could eliminate the need to counterbore the sight of the sight block by remove material from the back side of the sight drum. This amount would be dependant on the thickness across the outside ears of the sight block. You would think they all were the same but look at all the different thread pitches. If you couldn't remove quite enough material then the cross hole in the windage adjustment screw would need to be relocated. You can leave the A2 Screw length alone but it sticks out past the A1 sight drum about 1/8".
Then, the only drilling mod is the hole for the drun detent. Careful layout and manipulation could get this done without the use of expensive tools. The angle on the detent pin could be filed with a little trial and error.
The slit in the aperture spring is simply cut with a thin diameter cut-off wheel in a rotary tool.
Food for thought
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