1903A3 rear sight

[wantabe]

My rear sight on my James River 1903A3 looks new, but very time I shoot it aperture slides down. I have tightened small screw as much as I can. I'm shooting 150 grains at 2700 FPS.
Low recoil. Any thoughts on how I can fix this problem?

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[Johnny Peppers]

Try taking the tension spring off and bending the edges down slightly.