VTAC light mount:
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And Streamlight rail adapter:
h ttps://911supply.ca/component/page,shop.product_details/category_id,449/flypage,shop.flypage/product_id,839/option,com_virtuemart/Itemid,1/
Good combo for quickly mounting / removing a 1" diameter light from your shotgun. If you have the right kind of tube.
EDIT: with this light w ww.streamlight.com/product/product.aspx?pid=254