The larger front bead definitely will make it shoot lower. I have done this myself on a shotgun that had a plain barrel, and no rib or front "ramp" for the bead. Even though I don't ever focus on the bead it's in my field of unfocused view and I'm aware of it. When this method was suggested to me I had serious doubts but ordered a couple larger beads in the right thread size and tried it anyway. It worked perfectly. Brought the pattern down several inches at 25 yards.
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