You will need this for the particular firearm you mention. budsgunshop.com/catalog/product_info.php/products_id/24034/Smith+%26+Wesson+3007346+S%26W+M%26P+40+Smith+%26+Wesson+%28S%26W%29+15+rd+Steel+Black+Body%2FF --- Or if you need more capacity this : b