i first purchased a regular 1.125" diameter shroud from jody at tacticool. however, i prefer the thicker look so i ordered a 1.375" shroud from him and am very happy with it. i found him through these forums where he is also a vendor.

Barrel Shrouds : Tacticool22, Tactical .22 Rifle Parts and Accessories

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od: xd9 3"&4", 15-22, 1911 .22