If the .45 Convertible is a distributor exclusive* FLAT TOP Blackhawk blue gun Cat# NVB-44X Mod # 5242 or NVB-455X 5240, it has a steel grip frame and ERH. If it's a regular production 45 Conv., standard Blackhawk blue gun Cat# BN-44X 0446, BN-455X 0463, BN-44XL 10446 or BN-455XL 10463 it has alum alloy grip frame and ERH. (L in the Cat # means internal lock).
So the blue Flat top will nominally weigh the same as the stainless gun. The standard production BH will be a couple of ounces lighter, but hardly noticeable in recoil IMHO.
*The Flat Tops also have the advantage of the chamber alignment pawl for easier loading and unloading.