The Brass Seattle Slug weighs in at 3.5 ounces.
Installed it on my Glock 23, .40 Cal. Immediately felt like it adds weight to the back of the pistol which balances it out and brings the muzzle up. Haven't had a chance to shoot any rounds yet, but it just feels better doing dry-fire drills and drawing from the holster. Didn't want to give a 5-star since I don't have range time evaluation.